Responses Of Soil Carbon And Nitrogen Nutrients, Enzyme Activities And Microbial Communities To Extreme Climate In Various Cultivation Ages From Tea Orchards

Global climate change in temperature and precipitation will produce soil drying/wetting cycle changes or modify water availability in the recent and next decades. These changes in climate can turn over the recycles of C and N in soil which are essential for the growth of plants and the emissions of greenhouse gas (CO2, CH4 and N2O). Frequent summer droughts, caused by climate change, have negatively affected the productivity and quality of tea orchard soil. Tea (Camellia sinensis L.) is an important cash crop in southern China, therefore it is important to examine the responses of soil nutrients, enzyme activity and microbial community structural shifts under such summer drought, extreme warming and re-wetting conditions in various cultivation ages. The pot method was utilized to investigate the soil quality of various cultivation ages with 0,10,30, and 50 years and the effects of extreme climate treatments on soil bacterial community from barren land and tea orchard in this study. These pots were incubated at 25℃, given two different water treatments (30% and 55% WFPS (water-filled pore space)) for 14 days and then transferred to constant temperature incubator with 35℃ and 40 ℃ for 14 days followed by re-wetting. Throughout the incubation period, soil samples were taken to measure the soil carbon, nitrogen content, extracellular enzyme activities and soil bacterial communities at 0,7, 14,15,21,28 and 31 days. The results in the research are showed as follows:1) Prior to the incubation period, nitrate nitrogen, ammonia nitrogen, microbial nitrogen, and the total organic carbon in the tea soil increased with cultivation age. The microbial carbon and the extracellular enzyme activities (ββ1,4-glucosidase activity related to soil carbon and N-acetylglucosaminidase and 1-leucine aminopetidase activity related to soil nitrogen were highest at the cultivation age of 30a. The soil planted by tea tress for almost 30 years has a better nutrient environment.2) Soil samples taken under drought conditions indicated that a period drought increased extracellular enzyme activities, soil organic carbon, soil nitrate nitrogen, and ammonia nitrogen contents while soil microbial carbon and extracellular enzyme activities declined. The treatment of drought can reduce the availability of soil carbon and nitrogen nutrients.3) Warming treatments had a significant influence on soil carbon and nitrogen nutrients of tea plantation. Extreme warming reduced the contents of soil total organic carbon, nitrate nitrogen, ammonia nitrogen, microbial carbon and the activity of extracellular enzyme activities related to nitrogen. But extracellular enzyme activities related to carbon increased with the warming treatment. Extreme warming can destroy the recycle of carbon and nitrogen in soil and produce negatively effects on soil bacterial community diversity.4) The simulation of rainfall had an actively effect on the resilience of soil bacterial structure in the tea soil and the reconstruction of carbon and nitrogen cycles.5) Throughout all incubation periods, the tea soil samples taken from a cultivation age of 30 years exhibited a relatively high amount of dissolved organic carbon, microbial nitrogen, nitrate nitrogen, and soil extracellular enzyme activities. Furthermore, compared with other 2 cultivated age groups, the variation extents of soil total organic carbon, dissolved organic carbon, microbial carbon and nitrogen the soil samples taken from a cultivation age of 30 were lower. Those results showed that a 30-year cultivation of the tea tree had a positive effect on the soil nutrients and quality。Modified farming mode should be used to improve the soil quality like applying organic fertilizer and so on.6) With the extreme climate treatments, soil enzyme activity and microbial community structural shifted inducing the change of soil carbon and nitrogen transformation process and soil carbon and nitrogen contents decreased. What’s more, soil carbon contents were related with soil nitrogen contents.