Fine Root Biomass, Production And Their Relationship With Environmental Factors Of Four Typical Plant Communities In Loess Plateau, China

Fine roots(≤2 mm) play a major role in biogeochemical cycles of ecosystems. By the methods of soil cores and ingrowth soil cores, we studied the biomass, annual production and their relationship with environmental factors of fine roots in 0~40 cm soil layers of four typical plant communities(Robinia pseudoacacia plantation, deciduous shrubs, typical grassland and desert grassland) in Loess Plateau, China. The main research results are as follows:1. Fine root biomass and vertical distributionThe spatial patterns of fine root biomass were negatively associated with increasing latitudes. The fine root biomass in the 0~40 cm soil layer of deciduous shrubs(220 g·m-2) was greater than that of other three vegetation types of Robinia pseudoacacia plantation(163 g·m-2), typical grassland(162 g·m-2) and desert grassland(79 g·m-2). In the 0~40 cm soil layer of typical grassland, the proportion of ≤1 mm fine root biomass(74.1%) was significantly higher than those in other three plant communities. The fine root biomass of all four plant communities were mainly distributed in the 0~10 cm soil layer and decreased with soil depth. In the 0~10 cm soil layer of typical grassland, the proportion of fine root biomass(44.1%) was significantly higher than those in other three plant communities. 2. Fine root production and turnover timeThe fine root production of four vegetation types were ranked in the order of typical grassland(315 g·m-2·a-1)> deciduous shrubs(249 g·m-2·a-1)> Robinia pseudoacacia plantation(219 g·m-2·a-1)> desert grassland(115 g·m-2·a-1). The fine root productions of the four plant communities were mainly concentrated in the 0~10 cm top soil layer and decreased with soil depth. In the 0~10 cm soil layer, the proportion of the annual production(40.4%) was the highest in typical grassland. Fine roots of typical grassland turned over faster than the other three plant communities.3. The relationship between fine root biomass, production and turnover with environmental factorsWhen all data were pooled, fine root biomass and production of four plant communities were related to climate variables. They increased with increasing mean annual temperature. The linear regression analysis showed a significant increase of fine root biomass and production at a rate of 61.8 g·m-2 and 82.1 g·m-2·a-1 per 1℃ of temperature along the entire geographic range in Loess Plateau, respectively. Fine root biomass and production also showed a significant correlativity with mean annual precipitation. The linear regression analysis showed a significant increase of fine root biomass and production at a rate of 42.3 g·m-2 and 62.1 g·m-2·a-1 per 100 mm·a-1 of precipitation along the entire geographic range in Loess Plateau, respectively. Fine root turnover time had weak positive correlations with mean annual temperature and precipitation. When all data were pooled, fine root biomass and production of four plant communities were also affected by soil variables. The fine root biomass of four plant communities were positively associated soil organic matter content. In addition to deciduous shrubs, the fine root biomass of plant communities were significantly correlated with soil total nitrogen. There were weak positive correlations between fine root biomass and soil nitrate nitrogen contents in four plant communities. Fine root biomass had significant correlations with soil ammonium nitrogen contents. Fine root production was significantly positively correlated soil organic matter content in four plant communities except for desert grassland. The fine root production of Robinia pseudoacacia plantation and typical grassland were significantly correlated with soil total nitrogen. There were weak positive correlations between fine root production and soil nitrate nitrogen contents. In addition to deciduous shrubs, the fine root production of four plant communities had significant correlations with soil ammonium nitrogen contents. When all data were pooled, fine root turnover time of four plant communities was irrelevant to soil variables.