Soil Water Stress Overrides the Boosting Effect of iWUE from Rising CO2 and temperature in Determining Plantation Mortality in Semi-arid Cold Area

The counteractive influence of atmospheric CO2 enrichment and drought stress on tree growth results in great uncertainty in growth patterns of planted forests in cold semi-arid regions. We used tree-ring chronology and carbon isotope analysis to track ecophysiological processes in reaction to environmental factors over the past four decades of Populus simonii plantations in cold semi-arid areas in northern China. Our results showed that the boosting effect of the rising atmospheric CO2 concentration (Ca) on iWUE and stem growth was more significant in declined stands. However, the increased iWUE did not negate tree dieback when water stress was present. Therefore, the BAI and iWUE deviation of different health status trees started from a very early age. Climatic factors showed limited influences on the stem growth of the poplar plantations. The inaccessibility of deep soil water due to site-specific soil conditions rendered the trees exposed to chronic soil water stress and constrained stomatal conductance and reduced the CO2 fertilization effect. Consequently, these stands experienced a lower stem growth rate. In summary, we suggest that soil moisture conditions the iWUE and growth sensitivity to global warming and thus portrays site-specific decline episodes of different degrees in drought-prone areas.

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Improvement of evapotranspiration estimates over arid and semi-arid regions with a physically based water stress constraint scheme

10.5194/egusphere-egu2020-12757 ◽

2020 ◽

Author(s):

Kun Zhang ◽

Donghai Zheng ◽

Yunquan Wang ◽

Gaofeng Zhu

Keyword(s):

Soil Moisture ◽

Water Stress ◽

Soil Water ◽

Arid Regions ◽

Bare Soil ◽

Stress Constraint ◽

Near Surface ◽

Soil Water Stress ◽

Physically Based ◽

Semi Arid

<p>In the arid and semi-arid regions, the bare soil evaporation dominates the total evapotranspiration (ET). To date, in most of the process-based ET models, the constraint on the actual evaporation from bare soil due to water stress is either related to an empirical function of near-surface humidity or represented by a water stress factor linked with surface soil moisture. However, the relative humidity (RH) shows a hysteretic effect on the ET event, and the relationship between soil water stress and soil moisture is nonlinear, usually leading to the overestimation of ET in arid and semi-arid regions. In this study, we plan to improve the ET estimates on dry land by implementing a physically-based water stress constraint method, which is developed by parameterizing the Buckingham-Darcy&#8217;s law and yielded an excellent performance with laboratory data. The physically-based water stress constraint scheme is further incorporated into two different ET models (i.e. PT-JPL, MOD16) to generate the global ET estimates, whereby the latest ERA5-land reanalysis data and MODIS NDVI\LAI is adopted as model inputs. We not only validate the simulated ET with available flux observations but also intercompare the performances of different schemes in estimating ET in the arid and semi-arid regions. This study will provide a new way to characterize the regional soil water stress on the ET estimates especially in the arid and semi-arid conditions.</p>

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Potassium Application Positively Modulates Physiological Responses of Cocoa Seedlings to Drought Stress

Agronomy ◽

10.3390/agronomy11030563 ◽

2021 ◽

Vol 11 (3) ◽

pp. 563

Author(s):

Esther Anokye ◽

Samuel T. Lowor ◽

Jerome A. Dogbatse ◽

Francis K. Padi

Keyword(s):

Water Stress ◽

Soil Water ◽

Chlorophyll Content ◽

Electrolyte Leakage ◽

Seedling Survival ◽

Biomass Accumulation ◽

Biomass Partitioning ◽

Chlorophyll Content And Fluorescence ◽

Physiological Functions ◽

Soil Water Stress

With increasing frequency and intensity of dry spells in the cocoa production zones of West Africa, strategies for mitigating impact of water stress on cocoa seedling survival are urgently required. We investigated the effects of applied potassium on biomass accumulation, physiological processes and survival of cocoa varieties subjected to water stress in pot experiments in a gauzehouse facility. Four levels of potassium (0, 1, 2, or 3 g/plant as muriate of potash) were used. Soil water stress reduced plant biomass accumulation (shoot and roots), relative water content (RWC), chlorophyll content and fluorescence. Leaf phenol and proline contents were increased under water stress. Additionally, compared to the well-watered conditions, soils under water stress treatments had higher contents of exchangeable potassium and available phosphorus at the end of the experimental period. Potassium applied under well-watered conditions reduced leaf chlorophyll content and fluorescence and increased leaf electrolyte leakage, but improved the growth and integrity of physiological functions under soil water stress. Potassium addition increased biomass partitioning to roots, improved RWC and leaf membrane stability, and significantly improved cocoa seedling survival under water stress. Under water stress, the variety with the highest seedling mortality accumulated the highest contents of phenol and proline. A significant effect of variety on plant physiological functions was observed. Generally, varieties with PA 7 parentage had higher biomass partitioning to roots and better seedling survival under soil moisture stress. Proportion of biomass partitioned to roots, RWC, chlorophyll fluorescence and leaf electrolyte leakage appear to be the most reliable indicators of cocoa seedling tolerance to drought.

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