AUTHOR=Tiemuerbieke Bahejiayinaer , Ma Jian-Ying , Sun Wei 

TITLE=Differential eco-physiological performance to declining groundwater depth in Central Asian C3 and C4 shrubs in the Gurbantunggut Desert

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1244555

DOI=10.3389/fpls.2023.1244555

ISSN=1664-462X

ABSTRACT=<p>Resources in water-limited ecosystems are highly variable and unpredictable, and the maintenance of functional diversity among coexisting species is a crucial ecological strategy through which plants mitigate environmental stress. The comparison of differential eco-physiological responses among co-occurring plants in harsh environments could help provide deep insights into the coexistence mechanisms of competing species. Two coexisting desert shrubs with different photosynthetic pathways (<italic>Haloxylon ammodendron</italic> and <italic>Tamarix ramosissima</italic>) were selected in the Gurbantunggut Desert located in northwest China. This study detected variations in the water sources, photosynthetic parameters, stem water status, and non-structural carbohydrates of the two shrubs at three sites with different groundwater table depths during the growing seasons of 2015 and 2016 to identify distinct eco-physiological performances in coexisting plants with different functional types under fluctuating water conditions. The water sources of <italic>H. ammodendron</italic> shifted from soil water to groundwater, while <italic>T. ramosissima</italic> extracted water mainly from deep soil layers at both sites. Significant reductions in carbon assimilation and stomatal conductance in <italic>H. ammodendron</italic> with deeper groundwater table depth were detected during most drought periods, but no significant decreases in transpiration rate were detected with declining groundwater table depth. For <italic>T. ramosissima</italic>, all of these gas exchange parameters decreased with the progression of summer drought, and their relative reduction rates were larger compared with those of <italic>H. ammodendron</italic>. The stem water status of <italic>H. ammodendron</italic> deteriorated, and the relative reduction rates of water potential increased with deeper groundwater, whereas those of <italic>T. ramosissima</italic> did not differ with greater groundwater depth. These findings indicated that prolonged drought would intensify the impact of declining groundwater depth on the eco-physiology of both shrubs, but the extent to which the shrubs would respond differed. The two shrubs were segregated along the water–carbon balance continuum: the C<sub>3</sub> shrub <italic>T. ramosissima</italic> maximized its carbon fixation at an enormous cost of water, while greater carbon fixation was achieved with far greater water economy for <italic>H. ammodendron</italic>. These results demonstrated that the two shrubs prioritized carbon gain and water loss differently when faced with limited water sources. These mechanisms might mitigate competitive stress and enable their coexistence.</p>