Responses Of Enzyme Stoichiometry Characteristics To Stocking Rates In The Stipa Breviflora Desert Steppe

Soil enzymes are secretions produced by soil biometabolic processes that participate in the nutrient cycle of ecosystems through organic matter mineralization,phosphorus uptake and nitrogen fixation.Soil enzymes are very sensitive to environmental changes and are indicators of changes in soil productivity and soil fertility.Soil enzyme stoichiometry ratio refers to the ratio of soil enzyme activities that mediate C,N,and P mineralization and can indicate resource limitation patterns in soils.Short-flowered needlegrass(Stipa breviflora)desert grassland is an important grassland type in Inner Mongolia,with fragile ecological environment and extremely sensitive response to climate change,and grazing is one of the most important utilization methods of this type of grassland.Investigating the effect of livestock loading rate on soil enzyme activity and its stoichiometric characteristics can help to further understand the nutrient transformation in the grazing ecosystem of desert prairie,and can enhance the prediction of soil carbon cycle and climate change feedback.This study was conducted on a long-term grazing platform(grazing started in 2004)in Siziwang Banner,Inner Mongolia,with short-flowered needlegrass desert grassland as the research object.The aim was to reveal the effect of grazing on soil microbial carbon and nutrient limitation in desert grassland,and to provide a basis for grassland grazing management.The main results are as follows:(1)Five enzyme activities(soil α-glucosidase,soil β-glucosidase,leucine myrosinase,soil N-acetyl-β-amino glucosidase,and alkaline phosphatase)for C,N,and P acquisition significantly decreased(P<0.05)with increasing stock loading rate;the stoichiometric ratio of soil carbon and nitrogen enzymes significantly increased while the stoichiometric ratio of soil nitrogen and phosphorus enzymes significantly decreased(P<0.05);microorganisms were(1)The C limitation and N limitation of microorganisms were significantly increased with the increase of livestock loading rate,and the limitation was more serious with the increase of livestock loading rate.(2)The soil water content tended to decrease,soil bulk weight and soil p tended to increase with increasing livestock loading rate;soil total nutrients(soil organic carbon,soil total nitrogen,soil total phosphorus)and fast-acting nutrients(soil soluble organic carbon,soil inorganic nitrogen,soil fast-acting phosphorus)all decreased significantly(P<0.05);soil carbon to nitrogen ratio and soil carbon to phosphorus ratio tended to increase,and the difference of soil nitrogen to phosphorus ratio was not significant.(3)The soil microbial quantity(microbial quantity carbon,microbial quantity nitrogen,microbial quantity phosphorus)decreased significantly(P<0.05)with the increase of livestock carrying rate;soil bacterial fungal diversity showed a decreasing trend;the highest relative abundance of bacterial groups was Actinomycetes,and the highest relative abundance of fungus groups was Cysticerca.(4)The driving factors of carbon limitation and nitrogen limitation in short-flowered needlegrass desert grassland soils were different;the main driving factor of carbon limitation was microbial amount of nitrogen,and the main driving factor of N limitation was microbial amount of phosphorus;the phylum Bacteroides contributed the most to nutrient limitation with 63.8% among bacteria,and the phylum Sphaeromycetes contributed the most to nutrient limitation with 38.6% among fungi.