Effects of stand age and soil organic matter quality on soil bacterial and fungal community composition in Larix gmelinii plantations, Northeast China

It is of great interest to elucidate the biogeographic patterns of soil microorganisms and their driving forces, which is fundamental to predicting alterations in microbial-mediated functions arising from environment changes. Although the vertical movement of dissolved organic matter (DOM) drives the cycle of nutrients such as soil carbon but, in the restored ecosystem, the relationship between DOM and soil microbial nutrient utilization remains to be determined. Here, we investigated the changes of soil microbial community at 0-40 cm depth profile in three stages (10-, 30-, 50-years) of succession in Larix olgensis plantations and the fluorescence spectrum composition of DOM. With the increase of soil depth, the signal source of microorganisms increases. In a coniferous forest soil environment, the possible main source of DOM in deep soil is the production of microbial metabolism. Difficulty in the decomposition of organic matter determines the distribution and composition of microorganisms. Increasing forest age makes bacteria and fungi more specific and bacterial-fungal associations greater. Overall, our work contributes to the understanding of factors underlying microbial community distribution in plantation forests and the importance of DOM quality in building microbial communities.

Plant Functional and Phylogenetic Diversity Regulate Ecosystem Multifunctionality in Semi-Arid Grassland During Succession

The relationship between biodiversity and ecosystem multifunctionality (EMF) is crucial for understanding the processes of ecological restoration in semi-arid regions. However, partitioning the relative influence of various biodiversity attributes, namely taxonomic, functional, and phylogenetic diversity, on EMF during secondary succession is still unclear. This study aimed to bridge the gap by employing field measurements and the chronosequence approach at 21 plots with different stand ages and precipitation conditions on the Loess Plateau of China. For diversity indices, we calculated the Shannon–Wiener diversity index, Simpson’s dominance index, Pielou evenness index, community weighted mean (CWM), functional variance (FDvar), and Faith’s phylogenetic diversity (PD) based on the empirically measured composition and traits of plant species. The EMF was expressed as the averaged value of eight function variables (including aboveground biomass, root biomass, soil total carbon, total nitrogen, and total phosphorus content, soil organic carbon, available nitrogen and available phosphorus content). The results showed that species evenness and CWM of leaf dry matter content (LDMC) significantly increased yet the CWM of specific leaf area (SLA) decreased with stand age, indicating the resource-use strategy of the plants became more conservative through succession into its later stages. The EMF increased with both stand age and mean annual precipitation. The structural equation model revealed that stand age, soil water content (SWC), and the multiple diversity indices altogether accounted for 56.0% of the variation in the EMF. PD and the CWMs of plant height and LDMC had positive effects on the EMF, and the FDvar of leaf nitrogen had negative effects on EMF. However, the Shannon Wiener diversity had no significant effect on the EMF. Our results suggest that functional and phylogenetic diversity are more important than taxonomic diversity in predicting EMF, and that multidimensional biodiversity indices should be jointly considered to better predict EMF during the succession of semiarid grasslands.

Variability in Soil Macronutrient Stocks across a Chronosequence of Masson Pine Plantations

Plantations play a vital role in the global nutrient cycle because they have large stocks of soil macronutrients. However, the impacts of plantations on soil macronutrient stocks combined with stand age and soil physicochemical properties have not been well quantified. We compared soil macronutrient stocks at soil depths of 0−20 and 20−40 cm across a 7-, 14-, 25-, and 30-year chronosequence of Masson pine (Pinus massoniana Lamb.) plantations. The results showed that the nitrogen (N), phosphorus (P), and potassium (K) stocks first increased and then decreased with stand age. The highest N and P stocks were observed in the 14-year-old plantation, and the 25-year-old plantation displayed the highest K stock. The C, N, and P stocks declined with increasing soil depth across all sites, whereas the reverse trend was found in the K stock. Carbon stocks were highest for all plantations, followed by the K, N, and P stocks. Plantation soils exhibited a higher C:P ratio and a lower P:K ratio at various soil depths. The dominant controlling factors for the soil macronutrient stocks varied significantly at different stand ages and soil depths according to statistical analysis. For the total soil system, the C stock was affected by the available nutrients, organic matter, and stoichiometry; the available nutrients and organic matter were the determinant factors of the N and P stocks. Aggregate stability could be the primary parameter affecting the K stock. Organic matter explained most of the variation in soil macronutrient stocks, followed by the P:K ratio and available K. Collectively, our results suggest that the response of soil macronutrient stocks to stand age and soil depth will be dependent on different soil physicochemical properties, and P and K may be important limiting factors in Masson pine plantation ecosystems.

Carbon, nitrogen, and phosphorus stoichiometry of organic matter in Swedish forest soils and its relationship with climate, tree species, and soil texture

While the carbon (C) content of temperate and boreal forest soils is relatively well studied, much less is known about the ratios of C, nitrogen (N), and phosphorus (P) of the soil organic matter, and the abiotic and biotic factors that shape them. Therefore, the aim of this study was to explore carbon, nitrogen, and organic phosphorus (OP) contents and element ratios in temperate and boreal forest soils and their relationships with climate, dominant tree species, and soil texture. For this purpose, we studied 309 forest soils with a stand age >60 years located all over Sweden between 56° N and 68° N. The soils are a representative subsample of Swedish forest soils with a stand age >60 years that were sampled for the Swedish Forest Soil Inventory. We found that the N stock of the organic layer increased by a factor of 7.5 from −2 °C to 7.5 °C mean annual temperature (MAT), it increased almost twice as much as the organic layer stock along the MAT gradient. The increase in the N stock went along with an increase in the N : P ratio of the organic layer by a factor of 2.1 from −2 °C to 7.5 °C MAT (R2 = 0.36, p < 0.001). Forests dominated by pine had higher C : N ratios in the litter layer and mineral soil down to a depth of 65 cm than forests dominated by other tree species. Further, also the C : P ratio was increased in the pine-dominated forests compared to forests dominated by other tree species in the organic layer, but the C : OP ratio in the mineral soil was not elevated in pine forests. C, N and OP contents in the mineral soil were higher in fine-textured soils than in coarse-textured soils by a factor of 2.3, 3.5, and 4.6, respectively. Thus, the effect of texture was stronger on OP than on N and C, likely because OP adsorbs very rigidly to mineral surfaces. Further, we found, that the P and K concentrations of the organic layer were inversely related with the organic layer stock. The C and N concentrations of the mineral soil were best predicted by the combination of MAT, texture, and tree species, whereas the OP concentration was best predicted by the combination of MAT, texture and the P concentration of the parent material in the mineral soil. In the organic layer, the P concentration was best predicted by the organic layer stock. Taken together, the results show that the N : P ratio of the organic layer was most strongly related to MAT. Further, the C : N ratio was most strongly related to dominant tree species, even in the mineral subsoil. In contrast, the C : P ratio was only affected by dominant tree species in the organic layer, but the C : OP ratio in the mineral soil was hardly affected by tree species due to the strong effect of soil texture on the OP concentration.

The main drivers for the occurrence of six red-listed epiphytic bryophytes and lichens in the boreo-nemoral forest landscape, Latvia

Forest landscape plays a significant role in rare cryptogam distribution. However, data about the environmental demands of rare epiphytic bryophytes and lichens in boreo-nemoral forest landscapes are not complete. In this study, we focused on finding the main environmental predictors influencing the occurrence of three red-listed epiphytic bryophytes and three red-listed epiphytic lichens in the Latvian boreo-nemoral forest landscape. We obtained the records of species from the Natural Data Management System OZOLS database, which is a national information system on all rare taxa. We analyzed the occurrence of species in relation to forest stand age and area, forest type, heterogeneity and tree bark pH class. We found that selected red-listed bryophyte and lichen occurrence was mainly influenced by forest stand age and area. However, each of the red-listed epiphytic bryophyte and lichen has their own ecological demands in the boreo-nemoral landscape.

Growth of Managed Older Douglas-fir Stands: Implications of the Black Rock Thinning Trial in the Coast Range of Western Oregon

The most recent remeasurement of growth (at approximate total stand age 100 years) from the Black Rock Thinning Trial in western Oregon provides useful information for forest owners interested in accelerating restoration of older forest characteristics in Douglas-fir stands of the Pacific Northwest. Thinnings at several intensities at total stand age of roughly 50 years effectively reset stand growth patterns. With quadratic mean diameters in thinned plots up to 40% higher than those of unthinned controls, thinned plot mean annual increments (MAIs) and periodic annual increments continue to rise 55 years after thinning, with the peak in board foot and cubic foot MAI apparently still decades in the future. Assuming repeatable future thinning responses similar to the Black Rock Trial, financial analysis of the opportunity costs of extending rotations to 100 years indicates that some thinning treatments can reduce opportunity costs by up to half at a 6% discount rate. Study Implications Active management through thinning may be a useful tool for public and private landowners interested in rapid development of stands with older forest characteristics to enhance output of some ecosystem services. Heavy thinning regimes, of the type described here, are compatible with growing trees with large diameter stems, large branches, and large crowns. They also reduce fuel accumulation by lowering mortality rates of stems less than 60 years old and slowing the rate of crown recession, branch mortality, and branch litterfall. Midrotation thinning revenues reduce opportunity costs of holding more rapidly growing stems to older ages, which may be a consideration for some owners.

Soil Microbial Resource Limitations and Community Assembly Along a Camellia oleifera Plantation Chronosequence

Understanding soil microbial element limitation and its relation with the microbial community can help in elucidating the soil fertility status and improving nutrient management of planted forest ecosystems. The stand age of a planted forest determines the aboveground forest biomass and structure and underground microbial function and diversity. In this study, we investigated 30 plantations of Camellia oleifera distributed across the subtropical region of China that we classified into four stand ages (planted &lt;9 years, 9–20 years, 21–60 years, and &gt;60 years age). Enzymatic stoichiometry analysis showed that microbial metabolism in the forests was mainly limited by C and P. P limitation significantly decreased and C limitation slightly increased along the stand age gradient. The alpha diversity of the soil microbiota remained steady along stand age, while microbial communities gradually converged from scattered to clustered, which was accompanied by a decrease in network complexity. The soil bacterial community assembly shifted from stochastic to deterministic processes, which probably contributed to a decrease in soil pH along stand age. Our findings emphasize that the stand age regulated the soil microbial metabolism limitation and community assembly, which provides new insight into the improvement of C and P management in subtropical planted forest.