The worldwide allometric relationship in anatomical structures for plant roots.

The cortex (i.e., absorptive tissue) and stele (transportive vascular tissue) are fundamental to the function of plant roots. Unraveling how these anatomical structures are assembled in absorptive roots is essential for our understanding of plant ecology, physiology, and plant responses to global environmental changes. In this review, we first compile a large data set on anatomical traits in absorptive roots, including cortex thickness and stele radius, across 698 observations and 512 species. Using this data set, we reveal a common root allometry in absorptive root structures, i.e., cortex thickness increases much faster than stele radius with increasing root diameter (hereafter, root allometry). Root allometry is further validated within and across plant growth forms (woody, grass, and liana species), mycorrhiza types (arbuscular mycorrhiza, ectomycorrhiza, and orchid mycorrhizas), phylogenetic gradients (from ferns to Orchidaceae), and environmental change scenarios (e.g., elevation of atmospheric CO2 concentration and nitrogen fertilization). These findings indicate that root allometry is common in plants. Importantly, root allometry varies greatly across species. We then summarize recent research on the mechanisms of root allometry and potential issues regarding these mechanisms. We further discuss ecological and evolutionary implications of root allometry. Finally, we propose several important research directions that should be pursued regarding root allometry.

Leaf hydraulics coordinated with leaf economics and leaf size in mangrove species along a salinity gradient.

Independence among leaf economics, leaf hydraulics and leaf size confers plants great capability in adapting to heterogeneous environments. However, it remains unclear whether the independence of the leaf traits revealed across species still holds within species, especially under stressed conditions. Here, a suite of traits in these dimensions were measured in leaves and roots of a typical mangrove species, Ceriops tagal, which grows in habitats with a similar sunny and hot environment but different soil salinity in southern China. Compared with C. tagal under low soil salinity, C. tagal under high soil salinity had lower photosynthetic capacity, as indicated directly by a lower leaf nitrogen concentration and higher water use efficiency, and indirectly by a higher investment in defense function and thinner palisade tissue; had lower water transport capacity, as evidenced by thinner leaf minor veins and thinner root vessels; and also had much smaller single leaf area. Leaf economics, hydraulics and leaf size of the mangrove species appear to be coordinated as one trait dimension, which likely stemmed from co-variation of soil water and nutrient availability along the salinity gradient. The intraspecific leaf trait relationship under a stressful environment is insightful for our understanding of plant adaption to the multifarious environments.

Altitudinal variations and seasonal dynamics of near-surface and soil temperatures in subtropical forests of Mt. Guanshan, Jiangxi Province, China.

Temperature lapse rate (TLR), measured as the degree of temperature change along an altitudinal gradient, is a key indicator of multiple ecological processes of mountain systems. Although many studies have examined temperature changes of open air or near-surface along altitudes, we know little about altitudinal variations of soil temperature, which play an important role in regulating growth and reproduction of organisms, as well as ecosystem nutrient cycling. Based on temperature data of near-surface (15 cm above ground) and soil layers (8 cm below ground) from 12 sampling sites of subtropical forest along an altitudinal gradient (300-1300 m) in Jiangxi Guan-shan National Nature Reserve from September 2018 to August 2021, we calculated the lapse rates of mean, maximum, and minimum temperatures, as well as accumulated temperatures by using simple linear regression for both near-surface and soil temperature. The seasonal dynamics of aforementioned variables were also evaluated. The results showed that there were large differences among mean, maximum, and minimum lapse rates for annual near-surface temperature, which were 0.38, 0.31 and 0.51 ℃·(100 m)-1, respectively. But little variation was documented for soil temperature which were 0.40, 0.38 and 0.42 ℃·(100 m)-1, respectively. The seasonal variations of temperature lapse rates for near-surface and soil layers were minor except for minimum temperature. The lapse rates of minimum temperature were deeper in spring and winter for near-surface and in spring and autumn for soil layers. For growing degree days (GDD), the accumulated temperature under both layers were negatively correlated with altitude, and the lapse rates of ≥5 ℃ were 163 ℃·d·(100 m)-1 for near-surface and 179 ℃·d·(100 m)-1 for soil. The ≥5 ℃ GDD in soil were about 15 days longer than that in near-surface at the same altitude. The results showed inconsistent patterns of altitudinal variations between near-surface and soil temperature. Soil temperature and its lapse rates had minor seasonal variations compared with the near-surface counterparts, which was related to the strong buffering capacity of soil.

[Addition effects of co-expansion of two bamboos on plant diversity in broad-leaved forests]. / ç«¹å­æ‰©å¼ å¯¹é˜”å¶æž—ç‰©ç§å¤šæ ·æ€§çš„å½±å“ï¼šä¸¤ç«¹ç§çš„å åŠ æ•ˆåº”.

The effects of Phyllostachys edulis and Oligostachyum oedogonatum expansion on species diversity of broad-leaved forests were investigated in Wuyishan National Nature Reserve, Jiangxi Province, China. Ph. edulis and/or O. oedogonatum expansion changed community structure and species composition. The co expansion of the two bamboos in high intensity (Ph. edulis was 30-50 ind·100 m-2, O. oedogonatum was 300-500 ind·100 m-2) changed the density ratio of arbor and shrub from 2:8 to 1:9, and density ratio of bamboo and tree from 0:10 to 9:1. The main effects of Ph. edulis and O. oedogonatum on the species diversity were significant. Ph. edulis mainly influe-nced arbor layer, while O. oedogonatum influenced shrub layer more, and the interaction effect of two bamboos was not remarkable. There existed addition effects between Ph. edulis and O. oedogonatum on species diversity. The co-occurrence of two bamboos in high intensity decreased the Shannon index of community by 91.3%. Ph. edulis and O. oedogonatum did not compete obviously unless in high density. It was addition effect rather than interaction effect that changed the community structure and reduced species diversity when broad leaved forest suffered invasion by Ph. edulis and O. oedogonatum.

Accessing the impacts of bamboo expansion on NPP and N cycling in evergreen broadleaved forest in subtropical China.

Bamboo (Phyllostachys pubescens) expansion into adjacent forests is a widespread phenomenon in subtropical regions, and it has greatly changed the dominance hierarchy from trees to bamboos. This process may be accompanied by changes in productivity, nutrients accumulation and biogeochemical cycles. We compared the net primary production (NPP) and major pools and fluxes of nitrogen (N) in bamboo-dominant forest (BDF) and neighboring secondary evergreen broadleaved forest (EBF) in South China using the space-for-time substitution method. We found that the mean NPP of the BDF was 30.0 t ha-1 yr-1, which was 51.5% greater than that of the EBF (19.8 t ha-1 yr-1). The plant N pool for the BDF was 37.5% larger than that of the EBF, whereas the soil inorganic N pool significantly decreased by 31.2% with conversion of the EBF to BDF. Additionally, the ratio of N return to N uptake was 0.69 in the BDF and 0.88 in the EBF because of the lower litter N return of the BDF compared with that of the EBF. These results indicated that the expansion of P. pubescens significantly increased the NPP and plant N accumulation but reduced the soil N available pool and slowed the N cycling rate, which could lead to soil degradation.

Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China.

The impact of reforestation on soil organic carbon (OC), especially in deep layer, is poorly understood and deep soil OC stabilization in relation with aggregation and vegetation type in afforested area is unknown. Here, we collected topsoil (0-15 cm) and deep soil (30-45 cm) from six paired coniferous forests (CF) and broad-leaved forests (BF) reforested in the early 1990s in subtropical China. Soil aggregates were separated by size by dry sieving and OC stability was measured by closed-jar alkali-absorption in 71 incubation days. Soil OC concentration and mean weight diameter were higher in BF than CF. The cumulative carbon mineralization (Cmin, mg CO2-C kg-1 soil) varied with aggregate size in BF and CF topsoils, and in deep soil, it was higher in larger aggregates than in smaller aggregates in BF, but not CF. The percentage of soil OC mineralized (SOCmin, % SOC) was in general higher in larger aggregates than in smaller aggregates. Meanwhile, SOCmin was greater in CF than in BF at topsoil and deep soil aggregates. In comparison to topsoil, deep soil aggregates generally exhibited a lower Cmin, and higher SOCmin. Total nitrogen (N) and the ratio of carbon to phosphorus (C/P) were generally higher in BF than in CF in topsoil and deep soil aggregates, while the same trend of N/P was only found in deep soil aggregates. Moreover, the SOCmin negatively correlated with OC, total N, C/P and N/P. This work suggests that reforested vegetation type might play an important role in soil OC storage through internal nutrient cycling. Soil depth and aggregate size influenced OC stability, and deep soil OC stability could be altered by vegetation reforested about 20 years.

[Species-abundance distribution patterns along succession series of Phyllostachys glauca forest in a limestone mountain].

To detect the ecological process of the succession series of Phyllostachys glauca forest in a limestone mountain, five niche models, i.e., broken stick model (BSM), niche preemption model (NPM), dominance preemption model (DPM), random assortment model (RAM) and overlap- ping niche model (ONM) were employed to describe the species-abundance distribution patterns (SDPs) of 15 samples. χ² test and Akaike information criterion (AIC) were used to test the fitting effects of the five models. The results showed that the optimal SDP models for P. glauca forest, bamboo-broadleaved mixed forest and broadleaved forest were DPM (χ² = 35.86, AIC = -69.77), NPM (χ² = 1.60, AIC = -94.68) and NPM (χ² = 0.35, AIC = -364.61), respectively. BSM also well fitted the SDP of bamboo-broadleaved mixed forest and broad-leaved forest, while it was unsuitable to describe the SDP of P. glauca forest. The fittings of RAM and ONM in the three forest types were all rejected by the χ² test and AIC. With the development of community succession from P. glauca forest to broadleaved forest, the species richness and evenness increased, and the optimal SDP model changed from DPM to NPM. It was inferred that the change of ecological process from habitat filtration to interspecific competition was the main driving force of the forest succession. The results also indicated that the application of multiple SDP models and test methods would be beneficial to select the best model and deeply understand the ecological process of community succession.

[Effects of Phyllostachys edulis expansion on soil nitrogen mineralization and its availability in evergreen broadleaf forest].

By the methods of space-time substitution and PVC tube closed-top in situ incubation, this paper studied the soil mineralized-N content, N mineralization rate, and N uptake rate in Phyllostachys edulis-broadleaf mixed forest (PBMF) formed by P. edulis expansion and its adjacent evergreen broadleaf forest (EBF) in Dagangshan Mountain of Jiangxi Province, China. There existed the same spatiotemporal variation trend of soil total mineralized-N (TMN) content between the two forests. The annual average N mineralization rate was slightly lower in PBMF than in EBF. In PBMF, soil N mineralization was dominated by ammonification; while in EBF, soil ammonification and nitrification were well-matched in rate, and soil nitrification was dominated in growth season (from April to October). The N uptake by the plants in PBMF and EBF in a year was mainly in the form of NH4+-N, but that in EBF in growth season was mainly in the form of NO3- -N. These findings indicated that the expansion of P. edulis into EBF could promote the ammonification of soil N, weakened soil nitrification and total N mineralization, and also, increased the NH4+-N uptake but decreased the NO3- -N and TMN uptake by the plants.

[Soil respiration in subtropical forests and model simulation of its relationships with soil temperature and moisture content].

By using Li-6400-09 system, an in situ measurement on the soil respiration, soil temperature, and soil moisture content in three main forest types (evergreen broadleaved forest, Cunninghamia lanceolata plantation, and Phyllostachys pubescens forest) in subtropical area of China was conducted, with the relationships between soil respiration and soil temperature and moisture content simulated by several models. The C flux of soil respiration in P. pubescens forest, evergreen broadleaved forest, and C. lanceolata plantation was 12.84, 11.70, and 7.12 t C x hm(-2) x a(-1), respectively, and the soil respiration in these three forest types had similar diurnal and seasonal variations, with the maximum value at 11:00-12:00 and the minimum value at 1:00-3:00, and the highest value in August and September while the lowest value in December and January. Van't Hoff equation and Lloyd & Taylor function had less difference in describing the relationships between soil respiration and soil temperature, while the soil respiration rate predicted by Lloyd & Taylor function was smaller than the observed value. Quadratic model and power function model could well simulate the relationship between soil respiration and soil moisture content. Soil moisture content positively or negatively affected soil respiration, but the effects only reached significant level in C. lanceolata plantation. Comparing with single-factor equation, two-factor equation (soil temperature and moisture content) could better describe the responses of soil respiration to changed soil temperature and moisture content. Multivariate analysis of covariance showed that after eliminating the effects of soil temperature and moisture content, forest type had significant effects on soil respiration (R2 = 0.541). Other factors, such as air temperature, air relative humidity, and photosynthetic radiation also affected soil respiration, and the effects of air temperature reached significant level.