Hyposensitive canopy conductance renders ecosystems vulnerable to extreme droughts

2021 ◽  
Author(s):  
Hang Xu ◽  
Zhiqiang Zhang ◽  
Ram Oren ◽  
Xiaoyun Wu
Keyword(s):  
Hydraulic System ◽  
Arid Regions ◽  
Tree Mortality ◽  
Soil Drought ◽  
Canopy Conductance ◽  
Net Ecosystem Productivity ◽  
Vegetation Types ◽  
Drought Intensity ◽  
Stomatal Sensitivity ◽  
Water Use Strategy

Abstract Increased drought intensity with rising atmospheric demand for water (hereafter VPD) increases the risk of tree mortality worldwide. Ecosystem-scale water-use strategy (WUSe), quantified here by canopy stomatal sensitivity to VPD (Sc), is increasingly recognized as a factor in drought-related ecosystem dysfunction. However, the links between Sc and ecosystem adaptation to and stability following droughts are poorly established. We examined how Sc regulates carbon sequestration, identifying ecosystems potentially susceptible to drought-induced mortality based on data from the global flux network, remote-sensing products, and plant functional-traits archive. We found that Sc is higher where ecosystem water availability is low in arid regions, reflecting conservative WUSe (i.e., hypersensitivity), but ecosystems of all regions converge on permissive WUSe (i.e., hyposensitivity) under ample water supply. During extreme droughts, hyposensitive and hypersensitive ecosystems achieved similar net ecosystem productivity employing considerably different structural-functional strategies. However, hyposensitive ecosystems, risking their hydraulic system with permissive WUSe, did not recover from extreme droughts as quickly. Models predicting current performance and future distributions of vegetation types should account for the greater vulnerability of hyposensitive ecosystems to intensifying atmospheric and soil drought.

scholarly journals Research on Occurrence and Development of Pasture Drought Events in Alpine Grassland using the Drought Threshold

2018 ◽  
Author(s):  
Tiaofeng Zhang ◽  
Lin Li ◽  
Hongbin Xiao ◽  
Hongmei Li
Keyword(s):  
Soil Moisture ◽  
Alpine Grassland ◽  
Soil Drought ◽  
Severe Drought ◽  
Drought Event ◽  
Drought Intensity ◽  
Quantitative Expression ◽  
Initial Soil Moisture ◽  
Initial Soil ◽  
The Relationship

Abstract. Pasture is vital to livestock husbandry development in Qinghai and even in North China. Drought is the primary meteorological disaster that affects pasture, but insufficient soil moisture is the most prominent cause of pasture drought. Timely and accurate determination of the soil moisture threshold of pasture is important for objective recognition and monitoring of the occurrence and development of pasture drought. This study aims at investigating pasture responses to soil drought as well as quantitative expression of soil drought degree and drought threshold. Test plots were selected from the pasture test station. Five testing groups were set according to coverage rate (0–100 %) at the initiation the pasture growth period. The impacts of profile moisture characteristics, drought threshold, and precipitation on duration of pasture drought were studied. Research results have demonstrated that moisture in the soil profile below 20 cm decreases slightly throughout drought events in alpine grassland. Changes of soil moisture in the 0–20 cm layer can generally reflect drought stress of the pasture. In the process of a drought event, the relationship between soil water storage and cumulative relative water loss can be expressed via a logarithmic linear equation. Quantitative expression of drought degree in grasslands can be realized by transforming the slope of this equation into the index D with an interval of [0, 1]. The occurrence rates of mild drought,moderate drought, and severe drought were 0.36, 0.45, and 0.70, respectively. The duration of severe drought was closely related with initial soil moisture. The relationship between duration of drought and the necessary minimum precipitation can be expressed by an exponential equation. Values of the D index can express soil drought intensity and pasture drought intensity. The durations for different grades of drought events were correlated with both initial soil moisture and previous precipitation. The conclusions of this study can provide scientific references for the objective understanding onoccurrence, development, monitoring, and early warning of pasture drought.

Response pattern of amino compounds in phloem and xylem of trees to soil drought depends on drought intensity and root symbiosis

Plant Biology ◽  
2012 ◽  
Vol 15 ◽  
pp. 101-108 ◽  
Author(s):  
X.-P. Liu ◽  
C.-M. Gong ◽  
Y.-Y. Fan ◽  
M. Eiblmeier ◽  
Z. Zhao ◽  
...  
Keyword(s):  
Response Pattern ◽  
Soil Drought ◽  
Drought Intensity ◽  
Amino Compounds ◽  
Root Symbiosis

Application and limitations of the Artemisia/Chenopodiaceae pollen ratio in arid and semi-arid China

The Holocene ◽  
2012 ◽  
Vol 22 (12) ◽  
pp. 1385-1392 ◽  
Author(s):  
Yan Zhao ◽  
Hongyan Liu ◽  
Furong Li ◽  
Xiaozhong Huang ◽  
Jinghui Sun ◽  
...  
Keyword(s):  
Arid Regions ◽  
Positive Relationship ◽  
Vegetation Types ◽  
Pollen Data ◽  
Data Synthesis ◽  
Modern Pollen ◽  
Vegetation Zones ◽  
Desert Areas ◽  
Vegetation And Climate ◽  
Semi Arid

The Artemisia/Chenopodiaceae (A/C) ratio is assumed to be a useful index for reconstructing moisture changes in arid and semi-arid regions. Thorough modern pollen studies are still lacking to understand the reliability and limitation of A/C ratio as a moisture indicator, however. Here we review how well this ratio can be applied in arid and semi-arid China on the basis of new surface pollen data, previous data synthesis and other publications. Results indicate that variance in the A/C ratio can permit identification of modern vegetation types and that the A/C ratio generally has a positive relationship with annual precipitation. However, soil salinity, vegetation community composition, human activity and sample provenance (e.g. soil and lake sediments) will affect the values of the A/C ratio in different vegetation zones and therefore the A/C ratio is not comparable in different regions. We argue that the A/C ratio can only be used to reconstruct vegetation types and climate change in regions with precipitation <450–500 mm, and in steppe, steppe desert and desert areas. Careful studies should be undertaken to understand the modern pollen–vegetation–climate relationships in various regions before using the A/C ratio to interpret vegetation and climate.

scholarly journals Past and future scenarios of the effect of carbon dioxide on plant growth and transpiration for three vegetation types of southwestern France

2008 ◽  
Vol 8 (2) ◽  
pp. 397-406 ◽  
Author(s):  
J.-C. Calvet ◽  
A.-L. Gibelin ◽  
J.-L. Roujean ◽  
E. Martin ◽  
P. Le Moigne ◽  
...  
Keyword(s):  
Land Surface ◽  
Coniferous Forest ◽  
Land Surface Model ◽  
Co2 Concentration ◽  
Sensitivity Study ◽  
Surface Model ◽  
Canopy Conductance ◽  
Vegetation Types ◽  
Precipitation Regime ◽  
Annual Cycles

Abstract. The sensitivity of an operational CO2-responsive land surface model (the ISBA-A-gs model of Météo-France) to the atmospheric CO2 concentration, (CO2), is investigated for 3 vegetation types (winter wheat, irrigated maize, coniferous forest). Past (1960) and future (2050) scenarios of (CO2) corresponding to 320 ppm and 550 ppm, respectively, are explored. The sensitivity study is performed for 4 annual cycles presenting contrasting conditions of precipitation regime and air temperature, based on continuous measurements performed on the SMOSREX site near Toulouse, in southwestern France. A significant CO2-driven reduction of canopy conductance is simulated for the irrigated maize and the coniferous forest. The reduction is particularly large for maize, from 2000 to 2050 (−18%), and triggers a drop in optimum irrigation (−30 mm y−1). In the case of wheat, the response is more complex, with an equal occurrence of enhanced or reduced canopy conductance.

scholarly journals Predictors and mechanisms of the drought-influenced mortality of tree species along the isohydric to anisohydic continuum in a decade-long study of a central US temperate forest

2015 ◽  
Vol 12 (2) ◽  
pp. 1285-1325 ◽  
Author(s):  
L. Gu ◽  
S. G. Pallardy ◽  
K. P. Hosman ◽  
Y. Sun
Keyword(s):  
Water Potential ◽  
Leaf Water Potential ◽  
Tree Species ◽  
Tree Mortality ◽  
Leaf Water ◽  
Extreme Drought ◽  
Positive Temperature ◽  
Drought Intensity ◽  
Predawn Leaf Water Potential ◽  
Annual Variations

Abstract. Using decade-long continuous observations of tree mortality and predawn leaf water potential (ψpd) at the Missouri Ozark AmeriFlux (MOFLUX) site, we studied how the mortality of important tree species varied along the isohydric to anisohydric continuum and how such variations may be predicted. Water stress determined inter-annual variations in tree mortality with a time delay of one year or more, which was predicted by predawn leaf water potential integral (PLWPI), mean effective precipitation interval (a time period with no daily precipitation rates exceeding a threshold) with a daily threshold precipitation at 5 mm day−1 (MEPI5), and precipitation variability index (PVI). Positive temperature anomaly integral (PTAI) and vapor pressure deficit integral (VPDI) also worked reasonably well, particularly for moderate droughts. The extreme drought of the year 2012 drastically increased the mortality of all species in the subsequent year. Regardless of the degree of isohydry and drought intensity, the ψpd of all species recovered rapidly after sufficiently intense rain events. This, together with a lack of immediate leaf and branch desiccation, suggests that hydraulic disconnection in the xylem was absent even during extreme drought and tree death was caused by significant but indirect effects of drought. We also found that species occupying middle positions along the isohydric to anisohydric continuum suffered less mortality than those at either extremes (i.e. extremely isohydric or extremely anisohydric). Finally, our study suggested that species differences in mortality mechanisms can be overwhelmed and masked in extreme droughts and should be examined in a broad range of drought intensity.

Effects of seasonal and interannual climate variability on net ecosystem productivity of boreal deciduous and conifer forests

2002 ◽  
Vol 32 (5) ◽  
pp. 878-891 ◽  
Author(s):  
M A Arain ◽  
T A Black ◽  
A G Barr ◽  
P G Jarvis ◽  
J M Massheder ◽  
...  
Keyword(s):  
Populus Tremuloides ◽  
Land Surface ◽  
Black Spruce ◽  
Climatic Variability ◽  
Flux Measurement ◽  
Canopy Conductance ◽  
Net Ecosystem Productivity ◽  
Spruce Forest ◽  
Ecosystem Productivity ◽  
Aspen Forest

The response of net ecosystem productivity (NEP) and evaporation in a boreal aspen (Populus tremuloides Michx.) forest and a black spruce (Picea mariana (Mill.) BSP) forest in Canada was compared using a newly developed realistic model of surface-atmosphere exchanges of carbon dioxide (CO2), water vapor, and energy as well as eddy covariance flux measurements made over a 6-year period (1994-1999). The model was developed by incorporating a process-based two-leaf (sunlit and shaded) canopy conductance and photosynthesis submodel in the Canadian Land Surface Scheme (CLASS). A simple submodel of autotrophic and heterotrophic respiration was combined with the photosynthesis model to simulate NEP. The model performed well in simulating half-hourly, daily, and monthly mean CO2 exchange and evaporation values in both deciduous and coniferous forests. Modeled and measured results showed a linear relationship between CO2 uptake and evaporation, and for each kilogram of water transpired, approximately 3 g of carbon (C) were photosynthesized by both ecosystems. The model results confirmed that the aspen forest was a weak to moderate C sink with considerable interannual variability in C uptake. In the growing season, the C uptake capacity of the aspen forest was over twice that of the black spruce forest. Warm springs enhanced NEP in both forests; however, high mid-summer temperatures appear to have significantly reduced NEP at the black spruce forest as a result of increased respiration. The model suggests that the black spruce forest is a weak C sink in cool years and a weak C source in warm years. These results show that the C balance of these two forests is sensitive to seasonal and interannual climatic variability and stresses the importance of continuous long-term flux measurement to confirm modeling results.

scholarly journals Resistance of a lowland rain forest to increasing drought intensity in Sabah, Borneo

2004 ◽  
Vol 20 (6) ◽  
pp. 613-624 ◽  
Author(s):  
D. M. Newbery ◽  
M. Lingenfelder
Keyword(s):  
Growth Rates ◽  
Rain Forest ◽  
Tree Mortality ◽  
Mortality Rates ◽  
Stem Growth ◽  
Lowland Rain Forest ◽  
Drought Intensity ◽  
Tree Survival ◽  
Climatic Environment ◽  
Absolute Growth

Occasional strong droughts are an important feature of the climatic environment of tropical rain forest in much of Borneo. This paper compares the response of a lowland dipterocarp forest at Danum, Sabah, in a period of low (LDI) and a period of high (HDI) drought intensity (1986–96, 9.98 y; 1996–99, 2.62 y). Mean annual drought intensity was two-fold higher in the HDI than LDI period (1997 v. 976 mm), and each period had one moderately strong main drought (viz. 1992, 1998). Mortality of ‘all’ trees ≥10 cm gbh (girth at breast height) and stem growth rates of ‘small’ trees 10–<50 cm gbh were measured in sixteen 0.16-ha subplots (half on ridge, half on lower slope sites) within two 4-ha plots. These 10–50-cm trees were composed largely of true understorey species. A new procedure was developed to correct for the effect of differences in length of census interval when comparing tree mortality rates. Mortality rates of small trees declined slightly but not significantly between the LDI and HDI periods (1.53 to 1.48% y−1): mortality of all trees showed a similar pattern. Relative growth rates declined significantly by 23% from LDI to HDI periods (11.1 to 8.6 mm m−1 y−1): for absolute growth rates the decrease was 28% (2.45 to 1.77 mm y−1). Neither mortality nor growth rates were significantly influenced by topography. For small trees, across subplots, absolute growth rate was positively correlated in the LDI period, but negatively correlated in the HDI period, with mortality rate. There was no consistent pattern in the responses among the 19 most abundant species (n≥50 trees) which included a proposed drought-tolerant guild. In terms of tree survival, the forest at Danum was resistant to increasing drought intensity, but showed decreased stem growth attributable to increasing water stress.

scholarly journals Contrasting stomatal sensitivity to temperature and soil drought in mature alpine conifers

2019 ◽  
Vol 42 (5) ◽  
pp. 1674-1689 ◽  
Author(s):  
Richard L. Peters ◽  
Matthias Speich ◽  
Christoforos Pappas ◽  
Ansgar Kahmen ◽  
Georg Arx ◽  
...  
Keyword(s):  
Soil Drought ◽  
Stomatal Sensitivity

scholarly journals Leaf Shedding and Non-Stomatal Limitations of Photosynthesis Mitigate Hydraulic Conductance Losses in Scots Pine Saplings During Severe Drought Stress

2021 ◽  
Vol 12 ◽  
Author(s):  
Daniel Nadal-Sala ◽  
Rüdiger Grote ◽  
Benjamin Birami ◽  
Timo Knüver ◽  
Romy Rehschuh ◽  
...  
Keyword(s):  
Drought Stress ◽  
Scots Pine ◽  
Tree Mortality ◽  
Photosynthetic Apparatus ◽  
Simulation Models ◽  
Canopy Conductance ◽  
Severe Drought ◽  
Hydraulic Simulation ◽  
Leaf Shedding ◽  
Stomatal Limitations

During drought, trees reduce water loss and hydraulic failure by closing their stomata, which also limits photosynthesis. Under severe drought stress, other acclimation mechanisms are trigged to further reduce transpiration to prevent irreversible conductance loss. Here, we investigate two of them: the reversible impacts on the photosynthetic apparatus, lumped as non-stomatal limitations (NSL) of photosynthesis, and the irreversible effect of premature leaf shedding. We integrate NSL and leaf shedding with a state-of-the-art tree hydraulic simulation model (SOX+) and parameterize them with example field measurements to demonstrate the stress-mitigating impact of these processes. We measured xylem vulnerability, transpiration, and leaf litter fall dynamics in Pinus sylvestris (L.) saplings grown for 54 days under severe dry-down. The observations showed that, once transpiration stopped, the rate of leaf shedding strongly increased until about 30% of leaf area was lost on average. We trained the SOX+ model with the observations and simulated changes in root-to-canopy conductance with and without including NSL and leaf shedding. Accounting for NSL improved model representation of transpiration, while model projections about root-to-canopy conductance loss were reduced by an overall 6%. Together, NSL and observed leaf shedding reduced projected losses in conductance by about 13%. In summary, the results highlight the importance of other than purely stomatal conductance-driven adjustments of drought resistance in Scots pine. Accounting for acclimation responses to drought, such as morphological (leaf shedding) and physiological (NSL) adjustments, has the potential to improve tree hydraulic simulation models, particularly when applied in predicting drought-induced tree mortality.

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