scholarly journals The effect of rainfall amount and timing on annual transpiration in a grazed savanna grassland

2021 ◽  
Author(s):  
Matti Räsänen ◽  
Mika Aurela ◽  
Ville Vakkari ◽  
Johan P. Beukes ◽  
Juha-Pekka Tuovinen ◽  
...  
Keyword(s):  
Leaf Area ◽  
Gross Primary Production ◽  
Co2 Exchange ◽  
Wet Season ◽  
Area Index ◽  
C4 Grass ◽  
Precipitation Timing ◽  
Dry Spells ◽  
Annual Water

Abstract. The role of precipitation (P) variability on evapotranspiration (ET) and its two components, transpiration (T) and evaporation (E) from savannas, continues to draw significant research interest given its relevance to a number of eco-hydrological applications. Our study reports on six years of measured ET and estimated T and E from a grazed savanna grassland in Welgegund, South Africa. Annual P varied significantly in amount (508 to 672 mm yr−1), with dry years characterized by infrequent early-season rainfall. T was determined using annual water-use efficiency and gross primary production estimates derived from eddy covariance measurements of latent heat flux and net ecosystem CO2 exchange rates. The computed annual T was nearly constant, 331 ± 11 mm yr−1 (T/ET = 0.52), for the four wet years with frequent early wet-season rainfall, whereas annual T was 268 and 175 mm yr−1 during the dry years. Annual T/ET was linearly related to the early wet-season storm frequency. The constancy of annual T during wet years is explained by the moderate water stress of C4 grass and constant annual tree transpiration covering 15 % of the landscape. However, grass transpiration declines during dry spells. Moreover, grasses respond to water availability with a dieback-regrowth pattern, reducing leaf area and transpiration during drought. These changes lead to an anomalous monthly T/ET relation to leaf-area index (LAI). The results highlight the role of the C4 grass layer in the hydrological balance and suggest that the grass response to dry spells and drought is reasonably described by precipitation timing.

scholarly journals The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

2020 ◽  
Author(s):  
Matti Räsänen ◽  
Mika Aurela ◽  
Ville Vakkari ◽  
Johan P. Beukes ◽  
Juha-Pekka Tuovinen ◽  
...  
Keyword(s):  
Water Stress ◽  
Water Use ◽  
Temporal Dynamics ◽  
Gross Primary Production ◽  
Bare Soil ◽  
Co2 Exchange ◽  
C4 Grasses ◽  
Mature Trees ◽  
Area Index ◽  
Annual Water

Abstract. The role of precipitation (P) variability on evapotranspiration (ET) and its two components transpiration (T) and evaporation (E) rates from savannas continues to draw significant research interest given its relevance to a number of eco-hydrological applications. The work here reports on six years of measured ET and energy flux components, and estimated T from a grazed savanna grassland collected at a research site situated in Welgegund, South Africa. During this period, annual P varied considerably in amount (421 mm to 614 mm), rainy season length and precipitation intensity. T was estimated using annual water use efficiency and gross primary production determined from eddy-covariance measurements of net ecosystem CO2 exchange rates. The computed annual T was highly constrained to 352 ± 8 mm (T/ET = 0.55) for four wet years when rainfall was near or above the long-term mean. This is explained by the near constant annual tree transpiration and moderate water stress of C4 grasses during these years. In a drought year with intermittent rainfall, the annual ecosystem T was reduced due to grass dieback-regrowth that alters the temporal dynamics of bare soil cover and infiltration, and complicates monthly T/ET relation to leaf-area index (LAI). However, annual ET remains approximately equal to annual precipitation (P) even during the drought year due to increased soil evaporation. Indeed, at annual scales, ET ≈ P and annual T is conservative despite variation in amount and timing in rainfall, due to constant water use of mature trees, and the ability of C4 grasses to maintain transpiration at moderate water stress and effectively use pulsed rainfall.

Response of aboveground biomass increment, growth efficiency, and foliar nutrients to thinning, fertilization, and pruning in young Douglas-fir plantations in the central Oregon Cascades

1992 ◽  
Vol 22 (9) ◽  
pp. 1278-1289 ◽  
Author(s):  
Alejandro Velazquez-Martinez ◽  
David A. Perry ◽  
Tom E. Bell
Keyword(s):  
Leaf Area ◽  
Aboveground Biomass ◽  
Cultural Practices ◽  
Growth Efficiency ◽  
Douglas Fir ◽  
Nitrogen And Phosphorus ◽  
Area Index ◽  
Biomass Increment ◽  
Oregon Cascades

The effect of thinning and cultural practices (multinutrient fertilization, pruning) on total aboveground biomass increment and growth efficiency was studied over three consecutive 2-year periods (1981–1987) in young Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations. Net aboveground biomass increment over the 6-year period averaged 14.5, 7.8, and 5.5 Mg•ha−1•year−1 for the high-, medium-, and low-density plots, respectively. Growth efficiency, after dropping sharply between leaf area indexes of 1 and 6 m2/m2, remained relatively constant up to a leaf area index of 17, the highest measured. Consequently, aboveground biomass increment continued to increase at leaf area indexes well above that at which the Beer–Lambert law predicts maximum light should be absorbed. Foliage analyses indicate that thinning improved nitrogen, potassium, and magnesium nutrition and increased the translocation of potassium from 1-year-old foliage to support new growth. However, fertilization increased foliar nitrogen and phosphorus contents only when coupled with pruning, suggesting that trees favor total leaf area over individual needle nutrition. Indications of potassium and magnesium limitations in this study are supported by other recent studies in Douglas-fir. Further work on the role of multinutrient deficiencies in this species is warranted.

scholarly journals Numerical Assessments of Leaf Area Index in Tropical Savanna Rangelands, South Africa Using Landsat 8 OLI Derived Metrics and In-Situ Measurements

2019 ◽  
Vol 11 (7) ◽  
pp. 829 ◽  
Author(s):  
Timothy Dube ◽  
Santa Pandit ◽  
Cletah Shoko ◽  
Abel Ramoelo ◽  
Dominic Mazvimavi ◽  
...  
Keyword(s):  
South Africa ◽  
Leaf Area Index ◽  
Leaf Area ◽  
National Park ◽  
Dry Season ◽  
Kruger National Park ◽  
Landsat 8 ◽  
Tropical Savanna ◽  
Wet Season ◽  
Area Index

Knowledge on rangeland condition, productivity patterns and possible thresholds of potential concern, as well as the escalation of risks in the face of climate change and variability over savanna grasslands is essential for wildlife/livestock management purposes. The estimation of leaf area index (LAI) in tropical savanna ecosystems is therefore fundamental for the proper planning and management of this natural capital. In this study, we assess the spatio-temporal seasonal LAI dynamics (dry and wet seasons) as a proxy for rangeland condition and productivity in the Kruger National Park (KNP), South Africa. The 30 m Landsat 8 Operational Land Imager (OLI) spectral bands, derived vegetation indices and a non-parametric approach (i.e., random forest, RF) were used to assess dry and wet season LAI condition and variability in the KNP. The results showed that RF optimization enhanced the model performance in estimating LAI. Moderately high accuracies were observed for the dry season (R2 of 0.63–0.72 and average RMSE of 0.60 m2/m2) and wet season (0.62–0.63 and 0.79 m2/m2). Derived thematic maps demonstrated that the park had high LAI estimates during the wet season when compared to the dry season. On average, LAI estimates ranged between 3 and 7 m2/m2 during the wet season, whereas for the dry season most parts of the park had LAI estimates ranging between 0.00 and 3.5 m2/m2. The findings indicate that Kruger National Park had high levels of productivity during the wet season monitoring period. Overall, this work shows the unique potential of Landsat 8-derived metrics in assessing LAI as a proxy for tropical savanna rangelands productivity. The result is relevant for wildlife management and habitat assessment and monitoring.

scholarly journals Leaf Area Index identified as a major source of variability in modelled CO<sub>2</sub> fertilization

2018 ◽  
Author(s):  
Qianyu Li ◽  
Xingjie Lu ◽  
Yingping Wang ◽  
Xin Huang ◽  
Peter M. Cox ◽  
...  
Keyword(s):  
Primary Production ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Net Primary Production ◽  
Gross Primary Production ◽  
Vegetation Types ◽  
Cable Model ◽  
Co2 Fertilization ◽  
Area Index ◽  
Leaf Level

Abstract. The concentration-carbon feedback factor (β), also called the CO2 fertilization effect, is a key unknown in climate-carbon cycle projections. A better understanding of model mechanisms that govern terrestrial ecosystem responses to elevated CO2 is urgently needed to enable a more accurate prediction of future terrestrial carbon sink. We calculated CO2 fertilization effects at various hierarchical levels from leaf biochemical reaction, leaf photosynthesis, canopy gross primary production (GPP), net primary production (NPP), to ecosystem carbon storage (cpool), for seven C3 vegetation types in response to increasing CO2 under RCP 8.5 scenario, using the Community Atmosphere Biosphere Land Exchange model (CABLE). Our results show that coefficient of variation (CV) for the CABLE model among the seven vegetation types is 0.15–0.13 for the biochemical level β, 0.13–0.16 for the leaf-level β, 0.48 for the βGPP, 0.45 for the βNPP, and 0.58 for the βcpool. The low variation of the leaf-level β is consistent with a theoretical analysis that leaf photosynthetic sensitivity to increasing CO2 concentration is almost an invariant function. In CABLE, the major jump in CV of β values from leaf- to canopy- and ecosystem-levels results from divergence in modelled leaf area index (LAI) within and among the vegetation types. The correlations of βGPP, βNPP, or βcpool with βLAI are very high in CABLE. Overall, our results indicate that modelled LAI is a key factor causing the divergence in β values in CABLE model. It is therefore urgent to constrain processes that regulate LAI dynamics in order to better represent the response of ecosystem productivity to increasing CO2 in Earth System Models.

scholarly journals Influence of the Asian Monsoon on net ecosystem carbon exchange in two major plant functional types in Korea

2009 ◽  
Vol 6 (6) ◽  
pp. 10279-10309 ◽  
Author(s):  
H. Kwon ◽  
J. Kim ◽  
J. Hong
Keyword(s):  
Summer Monsoon ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Co2 Exchange ◽  
Plant Functional Types ◽  
Net Ecosystem Co2 Exchange ◽  
Area Index ◽  
Functional Types ◽  
Net Ecosystem Carbon Exchange

Abstract. Considering the feedback loops in radiation, temperature, and soil moisture with alterations in rainfall patterns, the influence of the changing monsoon on net ecosystem CO2 exchange can be critical to the estimation of carbon balance in Asia. In this paper, we examined the eddy covariance CO2 fluxes observed from 2004 to 2008 in two major plant functional types in KoFlux, i.e., the Gwangneung deciduous forest (GDK) site and the Haenam farmland (HFK) site. The objectives of the study were to (1) quantify the net ecosystem CO2 exchange (NEE), ecosystem respiration (RE), and gross primary production (GPP), (2) examine their interannual patterns, and (3) assess the mechanism for the coupling of carbon and water exchange associated with the summer monsoon. The GDK site, which had a maximum leaf area index (LAI) of ~5, was on average a relatively weak carbon sink with NEE of −84 gC m−2 y−1, RE of 1028 gC m−2 y−1, and GPP of 1113 gC m−2 y−1. Despite about 20% larger GPP (of 1321 gC m−2 y−1) in comparison with the GDK site, the HFK site (with the maximum LAI of 3 to 4) was a weaker carbon sink with NEE of −58 gC m−2 y−1 because of greater RE of 1263 gC m−2 y−1. In both sites, the annual patterns of NEE and GPP had a striking "mid-season depression" each year with two distinctive peaks of different timing and magnitude, whereas RE did not. The mid-season depression at the GDK site occurred typically from early June to late August, coinciding with the season of summer monsoon when the solar radiation decreased substantially due to frequent rainfalls and cloudiness. At the HFK site, the mid-season depression began earlier in May and continued until the end of July due to land use management (e.g., crop rotation) in addition to such disturbances as summer monsoon and typhoons. Other flux observation sites in East Asia also show a decline in radiation but with a lesser degree during the monsoon season, resulting in less pronounced depression in NEE. In our study, however, the observed depression in NEE changed the forest and farmland from a carbon sink to a source in the middle of the growing season. Consequently, the annually integrated values of NEE lies on the low end of the range reported in the literature. Such a delicate coupling between carbon and water cycles may turn these ecosystems into a stronger carbon sink with the projected trends of less frequent but more intensive rainfalls in this region.

scholarly journals The Effects of Zinc-Oxide Nanoparticles on Growth Parameters of Corn (SC704)

2015 ◽  
Vol 1 (2) ◽  
pp. 17-20 ◽  
Author(s):  
Melika Taheri ◽  
Hania Ataiei Qarache ◽  
Alimohammad Ataei Qarache ◽  
Mahdieh Yoosefi
Keyword(s):  
Plant Growth ◽  
Leaf Area ◽  
Irrigation Water ◽  
Dry Matter ◽  
Growth Parameters ◽  
Growth And Yield ◽  
Zno Nanoparticle ◽  
Area Index ◽  
Zno Particles

Nanoparticles are widely used in various fields like medicine and agriculture. Plant growth is hindered in mineral poor soils. Supplementing mineral poor soils can improve plant growth. One role of nanoparticles in agriculture is stimulating crop growth. In this study, the three different physical forms of ZnO particles in irrigation water were used to supplement mineral poor soil. Their effect on the growth of single cross 704 (SC704) corn was investigated. We studied the effects of ZnO nanocolloid, ZnO nanoparticles, and micrometric ZnO particles. The concentration of nanoparticles in irrigation water was 2 ppm. The results show that the addition of all three ZnO particle types in irrigation water improved shoot dry matter and leaf area index. The best results came from the ZnO nanoparticle treatment which on average, increased the shoot dry matter and leaf area indexes by 63.8% and 69.7% respectively. Based on these results, we can conclude that zinc nanoparticles can improve corn growth and yield in mineral poor soils.

scholarly journals Regional Leaf Area Index Retrieval Based on Remote Sensing: The Role of Radiative Transfer Model Selection

2015 ◽  
Vol 7 (4) ◽  
pp. 4604-4625 ◽  
Author(s):  
Gaofei Yin ◽  
Jing Li ◽  
Qinhuo Liu ◽  
Weiliang Fan ◽  
Baodong Xu ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Model Selection ◽  
Radiative Transfer ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Area Index

scholarly journals Quantification of ecohydrological sensitivities and their influencing factors at the seasonal scale

2021 ◽  
Vol 25 (3) ◽  
pp. 1447-1466
Author(s):  
Yiping Hou ◽  
Mingfang Zhang ◽  
Xiaohua Wei ◽  
Shirong Liu ◽  
Qiang Li ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Influencing Factors ◽  
Vegetation Change ◽  
Prediction Models ◽  
Edge Density ◽  
Wet Season ◽  
Slope Length ◽  
Area Index ◽  
Seasonal Scale

Abstract. Ecohydrological sensitivity, defined as the response intensity of streamflow to per unit vegetation change is an integrated indicator for assessing hydrological sensitivity to vegetation change. Understanding ecohydrological sensitivity and its influencing factors is crucial for managing water supply, reducing water-related hazards and ensuring aquatic functions by vegetation management. Yet, there is still a systematic assessment on ecohydrological sensitivity and associated driving factors especially at a seasonal scale lacking. In this study, 14 large watersheds across various environmental gradients in China were selected to quantify their ecohydrological sensitivities at a seasonal scale and to examine the role of associated influencing factors such as climate, vegetation, topography, soil and landscape. Based on the variables identified by correlation analysis and factor analysis, prediction models of seasonal ecohydrological sensitivity were constructed to test their utilities for the design of watershed management and protection strategies. Our key findings were the following: (1) ecohydrological sensitivities were more sensitive under dry conditions than wet conditions – for example, 1 % LAI (leaf area index) change, on average, induced 5.05 % and 1.96 % change in the dry and wet season streamflow, respectively; (2) seasonal ecohydrological sensitivities were highly variable across the study watersheds with different climate conditions, dominant soil types and hydrological regimes; and (3) the dry season ecohydrological sensitivity was mostly determined by topography (slope, slope length, valley depth and downslope distance gradient), soil (topsoil organic carbon and topsoil bulk density) and vegetation (LAI), while the wet season ecohydrological sensitivity was mainly controlled by soil (topsoil-available water-holding capacity), landscape (edge density) and vegetation (leaf area index). Our study provided a useful and practical framework to assess and predict ecohydrological sensitivities at the seasonal scale. The established ecohydrological sensitivity prediction models can be applied to ungauged watersheds or watersheds with limited hydrological data to help decision makers and watershed managers effectively manage hydrological impacts through vegetation restoration programs. We conclude that ecohydrological sensitivities at the seasonal scale are varied by climate, vegetation and watershed property, and their understanding can greatly support the management of hydrological risks and protection of aquatic functions.

scholarly journals A time-stepping scheme to simulate leaf area index, phenology, and gross primary production across deciduous broadleaf forests in eastern United States

2018 ◽  
Author(s):  
Qinchuan Xin ◽  
Yongjiu Dai ◽  
Xiaoping Liu
Keyword(s):  
United States ◽  
Time Series ◽  
Steady State ◽  
Primary Production ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Gross Primary Production ◽  
Eastern United States ◽  
Area Index ◽  
Time Stepping

Abstract. Terrestrial plants play a key role in regulating the exchange of energy and materials between the land surface and the atmosphere. Robust terrestrial biosphere models that simulate both time series of leaf dynamics and canopy photosynthesis are required to understand the vegetation-climate interactions. This study proposes a time stepping scheme to simulate leaf area index (LAI), phenology, and gross primary production (GPP) simultaneously via only climate variables based on an ecological assumption that plants allocate leaf biomass till an environment could sustain to maximize photosynthetic reproduction. The method establishes a linear function between the steady-state LAI and the corresponding GPP, which is used to track the suitability of environmental conditions for plant photosynthesis, and applies the MOD17 algorithm to form simultaneous equations together, which can be solved numerically. To account for the time lag in plant responses of leaf allocation to environment variation, a time stepping scheme is developed to simulate the LAI time series based on the solved steady-state LAI. The simulated LAI time series is then used to derive the timing of key phenophases and simulate canopy GPP with the MOD17 algorithm. The developed method is applied to deciduous broadleaf forests in eastern United States and has found to perform well on simulating canopy LAI and GPP at the site scale as evaluated using both flux tower and satellite data. The method could also capture the spatiotemporal variation of vegetation LAI and phenology across eastern United States as compared with satellite observations. The developed time-stepping scheme provides a simplified and improved version of our previous modeling approach and forms a potential basis for regional to global applications in future studies.

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