Nitrogenase activity of biological soil crusts and its response to hydrothermic factors in the Shapotou region of northern China

Aims In arid and semi-arid environments such as deserts,nitrogen is often the most limiting nutrient for biological activity.Biological soil crusts(BSCs) are an important component of vegetation in the Shapotou region in the Tengger Desert,northern China.However,their importance as contributors to soil fertility such as nitrogen fixation is relatively unknown.This study was conducted to quantify the potential nitrogenase activity(NA) of different types of BSCs in artificial vegetation areas,as well as their responses to variation in moisture and temperature.Methods Algae crust,lichen crust and moss crust were collected from an artificial vegetation area in the Shapotou region,and were incubated under three gradients of moisture(3,5 and 10 mm simulated rainfall) and temperature in open-top growth chambers from June to October.The NA was measured using acetylene reduction assay.One-way ANOVA and general linear models(GLM) procedure were applied to compare NA between treatments and interactions between type of BSCs,water and temperature.Important findings NA for each type of BSC was highly variable,ranging from 2.5 × 10 3 to 6.2 × 10 4 nmol C 2 H 4 ·m-2 ·h-1.The NA of algae crust was higher than that of lichen crust and moss crust(2.8 vs.2.4 and 1.4 × 10 4 nmol C 2 H 4 ·m-2 ·h-1,respectively).The three types of BSCs under the 3 mm simulated rainfall reached the maximum rate of nitrogen fixation,but 3 mm did not affect NA.Significant negative correlation was observed between NA of all three types of BSCs and temperature.The optimal temperature for NA in algae crust,moss crust and lichen crust were 25-30 °C,25-30 °C and 20-30 °C,respectively.