Contrasting responses of legume versus non-legume shrubs to soil water and nutrient shortages in the Mu Us Sandland

Legumes and non-legumes usually differ in using soil water and nutrients.Both water and nutrients are scarce in the semi-arid Mu Us Sandland where legume and/or non-legume shrubs coexist/dominate.Here,we addressed the responses of legume versus nonlegume shrubs to different soil water and nutrient conditions.Methods We conducted an experiment in which a legume(Hedysarum laeve)and a non-legume(Artemisia ordosica)were used,both of which are dominant species in the Mu Us Sandland.Seedlings of these two species were subjected to three water levels(45.0,67.5 and 90.0 ml every 3 days)and three nutrient treatments(0,0.1%and 0.2%nutrient solution every week)during the experiment.Important Findings Interactions between water and nutrients on total biomass,root weight ratio and rain use efficiency(RUE)were detected in A.ordosica but not in H.laeve,suggesting that water effects on A.ordosica but not on H.laeve are dependent on soil nutrients.Nutrient addition alleviated drought stress and increased RUE in A.ordosica.The interspecific differences in response to soil water and nutrients may be linked to the ability of plants to fix nitrogen.In addition,under lowsoil water or nutrient conditions,H.laeve produced more biomass than A.ordosica,and the opposite was the case under high-soil resources.The relationship between relative growth rate(RGR)and RUE[or nutrient use efficiency(NUE)]varied with two species.RGR of A.ordosica was positively correlated with both RUE and NUE while RGR of H.laeve was negatively correlated with NUE.The different responses may be linked to the trade-off between high-growth rate and low-resource use efficiency.