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Acid rain is one of most serious environment problems in China. The types of acid rain have gradually transformed from sulfuric acid rain (SAR) to mixed acid rain (MAR) and nitric acid rain (NAR) in recent years. Roots are one source of soil organic carbon and play an important role in the formation of soil aggregates. However, the changes in acid rain type and the effect of root removal on soil organic carbon in forest ecosystems are poorly understood. In this study, we removed roots and simulated acid rain with different types (SO42-: NO3- ratio of 4:1, 1:1, and 1:4) for three years in Cunninghamia lanceolata (CP) and Michelia macclurei ( MP) plantations to analyze the changes of soil organic carbon and physical properties and to measure the size and mean weight diameter ( MWD) of aggregates. Results showed that root removal in C. lanceolata and M. macclurei remarkably reduced soil organic carbon pool by 16.7 % and 21.5%, and soil recalcitrant carbon by 13.5% and 20.0%, respectively. Root removal substantially decreased the MWD and proportion and organic carbon content of soil macroaggregates in M. macclurei, but not in C. lanceolata. Acid rain did not affect soil organic carbon pool and soil aggregate structures. Our results indicated that roots promote soil organic carbon stabilization and that their contribution to the stability of soil organic carbon varies with forest types. Moreover, soil organic carbon stabilization is not affected by different types of acid rain in the short term. [ABSTRACT FROM AUTHOR]

Plants can alter soil microbial biomass and extracellular enzyme activities related with carbon (C), nitrogen (N), and phosphorus (P), through litter and root exudates, with consequences on soil carbon, nitrogen and phosphorus (P) cycling. However, it is not well known how the changes in soil phosphorus availability affect the relationships between plants and soil microorganisms. In this study, a factorial experiment was conducted to investigate the effects of Chinese fir (Cunninghamia lanceolata) planting and different levels of P addition (0, 1.95, 3.9, 7.8 and 15.6 g P ⋅ m-2 ⋅ a-1)on soil microbial biomass and extracellular enzyme activities. The results showed that planting Chinese fir planting significantly altered soil microbial biomass and C- and N- and P-related extracellular enzyme activities, but the effects were dependent on P addition levels. Without P addition, Chinese fir planting significantly reduced soil nutrient availability and pH, which led to the aggravation of P limitation and lower soil microbial biomass. P addition relieved P limitation, and reduced soil acid phosphatase (ACP) activities by 30.0%, 30.5%, 35.3% and 47.1% with the increasing P addition level (1.95, 3.9, 7.8 and 15.6 g P ⋅ m-2 ⋅ a-1). Under three P addition levels (1.95, 3.9 and 7.8 g P ⋅ m-2 ⋅ a-1), the negative effects of Chinese fir planting on soil microbial growth were alleviated. Under the high P addition level (15.6 g P ⋅ m-2 ⋅ a-1), the negative effects of Chinese fir planting on soil microbial growth occurred again due to soil N limitation. Taken together, Chinese fir planting and soil P availability generally affected soil microbial biomass and extracellular enzyme activities, and changed P limitation. [ABSTRACT FROM AUTHOR]

Stored nonstructural carbohydrates (NSC) indicate a balance between photosynthetic carbon (C) assimilation and growth investment or loss through respiration and root exudation. They play an important role in plant function and whole-plant level C cycling. CO2 elevation and nitrogen (N) deposition, which are two major environmental issues worldwide, affect plant photosynthetic C assimilation and C release in forest ecosystems. However, information regarding the effect of CO2 elevation and N deposition on NSC storage in different organs remains limited, especially regarding the trade-off between growth and NSC reserves. Therefore, here we analyzed the variations in the NSC storage in different organs of Chinese fir (Cunninghamia lanceolata) under CO2 elevation and N addition and found that NSC concentrations and contents in all organs of Chinese fir saplings increased remarkably under CO2 elevation. However, N addition induced differential accumulation of NSC among various organs. Specifically, N addition decreased the NSC concentrations of needles, branches, stems, and fine roots, but increased the NSC contents of branches and coarse roots. The increase in the NSC contents of roots was more pronounced than that in the NSC content of aboveground organs under CO2 elevation. The role of N addition in the increase in the structural biomass of aboveground organs was greater than that in the increase in the structural biomass of roots. This result indicated that a different trade-off between growth and NSC storage occurred to alleviate resource limitations under CO2 elevation and N addition and highlights the importance of separating biomass into structural biomass and NSC reserves when investigating the effects of environmental change on biomass allocation. [ABSTRACT FROM AUTHOR]