Abstract:

Aims Populus pruinosa is a key species of desert riparian forest playing an irreplaceable role in eco-environmental protection in Tarim extremely arid region, China. Studies on variation pattern of ecological stoichiometric characteristics and homeostasis of plant and soil were helpful to understand the health status of desert vegetation and also provide insights into ecosystem nutrient cycling, and ecological strategies of organisms to environmental changes. The aim of the present study was to explore the variations of ecological stoichiometry of plant and soil carbon (C), nitrogen (N), phosphorus (P) and their stoichiometric homeostasis of P. pruinosa leaves along groundwater depth (GWD) in Tarim basin.

Methods Through field investigation, we measured C, N, P contents in leaves of P. pruinosa and in soils. The differences between C, N, P contents and their stoichiometric ratios of leaves and soils as well as in stoichiometric homoeostasis were examined among sites with different groundwater depths.

Important findings With the increase of GWD, the N, P contents of leaves decreased and C content, C:N, C:P, N:P increased. The variation coefficient of all stoichiometric indices was basically low and that of C content was the lowest, but the difference among different GWD was significant. Leaf C content and C:P were significantly negative correlated with leaf N content, and leaf C:P and N:P were significantly negative correlated with leaf P content. Soil C, N, P contents and their stoichiometric ratios all decreased with the increase of GWD, and the variation coefficients of other indices except P content were high and significantly different among different GWDs. Soil P content was positively correlated with soil C and N contents. Moreover, the correlation of C, N, P stoichiometry between leaf and soil in shallow and middle GWD habitats were non-significant, while there were significant correlations between leaf P content, leaf N:P and soil stoichiometry indices in deep GWD habitats, and leaf C:N, C:P were higher in deep GWD habitats than that of other two habitats. It indicated that leaf stoichiometric characteristics were not directly determined by soil nutrient conditions, P. pruinoseimproved nutrient utilization to adapt arid adversity. The N and P stoichiometric homeostasis index (H) of P. pruinosa were ranked in the order of H_N > H_N:P > H_P. Combined with nutrient restriction diagnostic index (N:P), evidence suggested the growth of P. pruinosa was limited by P. Populus pruinosa maintained a relatively stable state of C content, N content, C:N, C:P with homeostasis regulation, adopting the conservative defense strategy to adapt to the increasingly arid environment. Therefore, adequate P supply should be considered during the restoration process in degraded desert riparian forests.

Key words: extreme arid region, groundwater depth, Populus pruinosa, soil, ecological stoichiometry, homoeostasis