Phosphorus addition increases microbial necromass by increasing N availability in China: A meta-analysis

Phosphorus (P) is an essential limiting nutrient which has a massive impact on soil organic carbon (SOC) dynamics. However, a general pattern reflecting the response of amino sugars which is an essential component of SOC to P addition in China is unclear. We conducted a meta-analysis using 24 observations in nine research publications to examine the changes in microbial necromass in response to P addition. The results indicated that P addition significantly increased total microbial (total amino sugars, TAS), fungal (glucosamine, GlcN), and bacterial (muramic acid, MurN) necromass. Effect of P addition on amino sugars depends on climate type, ecosystem type, P addition rate and P addition duration. P input can increase galactosamine (GalN), GlcN, and MurN in montane climate, whereas P addition only increased GalN and MurN in continental climates. Also, P addition significantly raised GalN and MurN in forest ecosystems, especially in plantation forests. Low P addition rates (0–50 kg P ha−1 yr−1) had positive effects on GalN and MurN. In addition, the medium P addition time (6–10 years) significantly increased GalN, GlcN, and MurN. We also found that natural log response ratio (lnRR) of soil available nitrogen (N) was positively correlated with lnRR of amino sugars suggesting that P application alleviates N limitation and reduces the uptake of N from microbial necromass leading to increased accumulation of microbial necromass. Unexpectedly, lnRR of microbial phospholipid fatty acids (PLFAs) poorly correlated with lnRR of amino sugars. This may be due to the bias caused by not having enough observations. Limited data set impeded our understanding of whether P-induced increase in amino sugars mainly attributable to increase in PLFAs and underlying mechanisms. Our meta-analysis had important implications on predicting the effect of P addition on amino sugars under different environmental conditions, providing invaluable information for soil fertility enhancement and SOC sequestration.