Root exudation stimulates microbial decomposition and enhances nutrient availability to plants. It remains difficult to measure and predict this carbon flux in natural conditions, especially for mature woody plants. Based on a known conceptual framework of root functional traits coordination, we proposed that root functional traits may predict root exudation. We measured root exudation and other seven root morphological/chemical/physiological traits for 18 coexisting woody species in a deciduous-evergreen mixed forest in subtropical China. Root exudation, respiration, diameter and nitrogen (N) concentration all exhibited significant phylogenetic signals. We found that root exudation positively correlated with competitive traits (root respiration, N concentration) and negatively with a conservative trait (root tissue density). Furthermore, these relationships were independent of phylogenetic signals. A principal component analysis showed that root exudation and morphological traits loaded on two perpendicular axes. Root exudation is a competitive trait in a multidimensional fine-root functional coordination. The metabolic dimension on which root exudation loaded was relatively independent of the morphological dimension, indicating that increasing nutrient availability by root exudation might be a complementary strategy for plant nutrient acquisition. The positive relationship between root exudation and root respiration and N concentration is a promising approach for the future prediction of root exudation.

Three hundred and nineteen 'Guanximiyou' pummelo (Citrus grandis) orchards from Pinghe county, the southern region of Fujian province, China, were selected for this study. The objectives were to determine (i) the soil and leaf nutrient status, (ii) the relationships between leaf mineral elements and the corresponding soil elements, and (iii) the relationships between fruit quality and mineral nutrients. The results showed that soil acidification was a major problem in these orchards, with an average pH of 4.34. Soil acidification affected the availability of soil N, P, Ca, Mg, S, B, Cu and Zn and the levels of organic matter (OM) and cation exchange capacity (CEC), thus inducing soil and leaf nutrient imbalance. Indeed, severe nutrient imbalance existed in these orchard soils. 77.4% and 65.8% of soils were sub-optimum in exchangeable Mg and Ca, while 96.6% and 82.1% of soils were super-optimum in available S and P, respectively. Besides, severe nutrient deficiencies and excesses co-existed in leaves. 46.8% and 35.6% of leaves were deficient in N and Mg, while 74.8% and 70.4% of leaves were excess in B and Cu, respectively. Regressive analysis showed that leaf content of mineral elements was poorly related with the available content of the corresponding soil elements, respectively. In some orchards, severe juice sac granulation, an important factor affecting fruit quality, was observed. Regressive analysis indicated that Mg, S, Cu and Mn played a role in juice sac granulation of fruits. In conclusion, soil acidification might lead to severe soil nutrient imbalance, thus inducing leaf nutrient imbalance, eventually impairing fruit quality parameters such sac granulation.

Arbuscular mycorrhizal (AM) fungi are widespread and ancient root-associated microorganisms (Davison et al., 2015; Lu & Hedin, 2019). They can form mycorrhizal symbiosis with plants and thus affect many important ecosystem processes (van der Heijden et al., 2015). The well-established function for AM fungi is to improve their host uptake of soil phosphorus (P) in exchange for plant carbon (C; Marschner & Dell, 1994). In addition, they can increase crop yield (Zhang et al., 2019), regulate plant diversity

Primary forest conversion is a worldwide serious problem associated with human disturbance and climate change. Land use change from primary forest to plantation, grassland or agricultural land may lead to profound alteration in the emission of soil greenhouse gases (GHG). Here, we conducted a global meta‐analysis concerning the effects of primary forest conversion on soil GHG emissions and explored the potential mechanisms from 101 studies. Our results showed that conversion of primary forest significantly decreased soil CO2 efflux and increased soil CH4 efflux, but had no effect on soil N2O efflux. However, the effect of primary forest conversion on soil GHG emissions was not consistent across different types of land use change. For example, soil CO2 efflux did not respond to the conversion from primary forest to grassland. Soil N2O efflux showed a prominent increase within the initial stage after conversion of primary forest and then decreased over time while the responses of soil CO2 and CH4 effluxes were consistently negative or positive across different elapsed time intervals. Moreover, either within or across all types of primary forest conversion, the response of soil CO2 efflux was mainly moderated by changes in soil microbial biomass carbon and root biomass while the responses of soil N2O and CH4 effluxes were related to the changes in soil nitrate and soil aeration‐related factors (soil water content and bulk density), respectively. Collectively, our findings highlight the significant effects of primary forest conversion on soil GHG emissions, enhance our knowledge on the potential mechanisms driving these effects and improve future models of soil GHG emissions after land use change from primary forest.

Summary The adoption of diverse resource acquisition strategies is critical for plant growth and species coexistence. Root phosphatase is of particular importance in the acquisition of soil phosphorus (P), yet it is often overlooked in studies of root trait syndromes. Here, we evaluated the role of root phosphatase activity (RPA) within the root economics space and the order‐based variation of RPA, as well as the correlations between RPA and a suite of leaf traits and soil properties over a range of evergreen tree species in a subtropical forest. Root phosphatase activity exhibited a high degree of inter‐specific variation. We found that there were two leading dimensions of the multidimensional root economics space, the root diameter–specific root length axis (collaboration trait gradient) and the root tissue density–root nitrogen concentration axis (classical trait gradient), and RPA aligned with the former. Root phosphatase activity is used as a ‘do it yourself’ strategy of soil P acquisition, and was found to be inversely correlated with mycorrhizal colonization, which suggests a trade‐off in plant P acquisition strategies. Compared with soil and foliar nutrient status, root traits mattered most for the large inter‐specific changes in RPA. Furthermore, RPA generally decreased from first‐ to third‐order roots. Taken together, such diverse P‐acquisition strategies are conducive to plant coexistence within local forest communities. The use of easily measurable root traits and their tight correlations with RPA could be a feasible and promising approach to estimating species‐specific RPA values, which would be helpful for better understanding plant P acquisition and soil P cycling.

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Global changes can alter plant inputs from both above-and belowground, which, thus, may differently affect soil carbon and microbial communities. However, the general patterns of how plant input changes affect them in forests remain unclear. By conducting a meta-analysis of 3193 observations from 166 experiments worldwide, we found that alterations in aboveground litter and/or root inputs had profound effects on soil carbon and microbial communities in forest ecosystems. Litter addition stimulated soil organic carbon (SOC) pools and microbial biomass, whereas removal of litter, roots or both (no inputs) decreased them. The increased SOC under litter addition suggested that aboveground litter inputs benefit SOC sequestration despite accelerated decomposition. Unlike root removal, litter alterations and no inputs altered particulate organic carbon, whereas all detrital treatments did not significantly change mineral-associated organic carbon. In addition, detrital treatments contrastingly altered soil microbial community, with litter addition or removal shifting it toward fungi, whereas root removal shifting it toward bacteria. Furthermore, the responses of soil carbon and microbial biomass to litter alterations positively correlated with litter input rate and total litter input, suggesting that litter input quantity is a critical controller of belowground processes. Taken together, these findings provide critical insights into understanding how altered plant productivity and allocation affects soil carbon cycling, microbial communities and functioning of forest ecosystems under global changes. Future studies can take full advantage of the existing plant detritus experiments and should focus on the relative roles of litter and roots in forming SOC and its fractions.

Root respiration is a critical physiological trait involved in root resource acquisition strategies, yet it is less represented in root trait syndrome. Here we compiled a large dataset of root respiration associated with root chemical and morphological traits from 245 plant species. Our results demonstrated that root respiration correlated positively with root nitrogen concentration (RNC) and negatively with root tissue density (RTD) across and within woody and non-woody species. However, the relationships between root respiration and specific root length (SRL) and root diameter (RD) were weak or even insignificant. Such root respiration-traits relationships were not completely in line with predictions by the root economics spectrum (RES). Furthermore, the principal component analysis showed that root trait syndrome was multidimensional. Root respiration was associated more strongly with the RNC-RTD axis (the classical RES) than with the orthogonal SRL-RD axis for woody species, but not for non-woody species. Collectively, the linkages of root physiological, chemical, and morphological traits provide a better understanding of root trait covariation and root resource acquisition strategies.