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Let's visit the evergreen forest
\"Winter lasts a long time in the evergreen forest biome. The trees here stay green all year. But how do tree needles help a tree survive the winter? And how do animals live in the snow and cold? Read this book to find out!\"--Provided by publisher.
Book
Differences in root exudate inputs and rhizosphere effects on soil N transformation between deciduous and evergreen trees
Background and aims
While the coupled effects of root exudates and microbial feedbacks on soil processes are well-recognized, we still lack an understanding of differences in root exudate fluxes and the associated ecological consequences among tree growth forms.
Methods
Two deciduous tree species (i.e.,
Cercidiphyllum japonicum
and
Larix kaempferi
) and two evergreen tree species (i.e.,
Pinus armandi
and
Pinus tabulaeformis
) were selected to perform an in-situ collection of root exudates during the growing season in 2016. The net N mineralization rates and associated microbial enzyme activities were measured in rhizosphere and bulk soils to evaluate rhizosphere effects. Moreover, we compiled the dataset related to root exudation and their associated biological traits and the soil chemical properties for 21 tree species from temperate forests.
Results
The root exudation rates and the annual root exudate carbon (C) fluxes of two deciduous tree species were significantly higher than those of the two evergreen tree species. Correspondingly, the rhizosphere effects of deciduous tree species on the microbial biomass, enzyme activity and net N mineralization rate were approximately 1.9, 1.6 and 2.4 times greater than those of the evergreen tree species, respectively. Rhizosphere effects were positively correlated with the root exudation rate. The compiled dataset also suggest that deciduous tree species tend to have higher exudation rates than evergreen tree species in temperate forests.
Conclusions
Collectively, these results suggest that the two tree growth forms exhibit different patterns in root exudate inputs and associated rhizosphere microbial processes. Generally, deciduous tree species tend to exude more C into the soil and consequently induce greater microbial feedback on soil N transformations during the growing season in temperate regions, implying that deciduous tree species induced a greater effect on the C and nutrient cycling in rhizosphere soil than evergreen tree species.
Journal Article
Effects of light and topography on regeneration and coexistence of evergreen and deciduous tree species in a Chinese subtropical forest
1. Evergreen broad-leaved forests are widely distributed in eastern Asia with evergreen broad-leaved (EBL) and deciduous broad-leaved (DBL) tree species coexisting under the same climatic regime, raising questions as to the underlying mechanisms. Since EBL and DBL species differ in leaf life span, a key component of resource economic strategies, their coexistence might be attributed to regeneration niche partitioning across habitats varying in resource supply. 2. We investigated the effects of variation in insolation and topography on regeneration of EBL and DBL species in a subtropical EBL forest of eastern China after an ice storm that caused severe canopy disturbance. 3. Using a mixed-effects modelling framework and census data from 2011 to 2014 on 8,548 wild seedlings of 123 species, we quantified habitat preferences of EBL and DBL species during post-disturbance regeneration and how their survival and height relative growth rates varied among habitats. 4. The relative density of DBL seedlings (proportional to all seedlings) was greater in habitats with greater (canopy gaps) compared to habitats with lesser (understorey) insolation and increased with canopy gap size. However, DBL seedlings were not more frequent in higher (valleys) compared to lower (ridges) fertility habitats. Although DBL seedlings exhibited larger differences in growth between higher and lower resource habitats than EBL seedlings, their growth rates did not increase with canopy gap size. Seedlings of EBL species had high survival in all habitats, but larger DBL seedlings survived equally well on ridges. Consequently, the relative density of DBL seedlings declined in valleys, so that by 2014 it became more similar in valley and ridge habitats, whereas it remained higher in gaps than in the understorey, and especially in larger gaps. 5. Synthesis. Specialization on contrasting topographic habitats is considered the primary mechanism mediating coexistence between deciduous broad-leaved and evergreen broad-leaved species. Our results, however, suggest this may not always be true, since seedlings of deciduous broad-leaved and evergreen broad-leaved species partitioned regeneration niches based on light more so than topography. We propose that coexistence of deciduous broad-leaved and evergreen broadleaved species can strongly depend upon canopy disturbance to create a mosaic of habitat patches, including high light gaps favouring regeneration of deciduous broad-leaved species.
Journal Article
Seasonal variation in the canopy color of temperate evergreen conifer forests
Evergreen conifer forests are the most prevalent land cover type in North America. Seasonal changes in the color of evergreen forest canopies have been documented with near-surface remote sensing, but the physiological mechanisms underlying these changes, and the implications for photosynthetic uptake, have not been fully elucidated. Here, we integrate on-the-ground phenological observations, leaf-level physiological measurements, near surface hyperspectral remote sensing and digital camera imagery, towerbased CO 2 flux measurements, and a predictive model to simulate seasonal canopy color dynamics. We show that seasonal changes in canopy color occur independently of new leaf production, but track changes in chlorophyll fluorescence, the photochemical reflectance index, and leaf pigmentation. We demonstrate that at winter-dormant sites, seasonal changes in canopy color can be used to predict the onset of canopy-level photosynthesis in spring, and its cessation in autumn. Finally, we parameterize a simple temperature-based model to predict the seasonal cycle of canopy greenness, and we show that the model successfully simulates interannual variation in the timing of changes in canopy color. These results provide mechanistic insight into the factors driving seasonal changes in evergreen canopy color and provide opportunities to monitor and model seasonal variation in photosynthetic activity using color-based vegetation indices.
Journal Article
Greenness indices from digital cameras predict the timing and seasonal dynamics of canopy-scale photosynthesis
The proliferation of digital cameras co-located with eddy covariance instrumentation provides new opportunities to better understand the relationship between canopy phenology and the seasonality of canopy photosynthesis. In this paper we analyze the abilities and limitations of canopy color metrics measured by digital repeat photography to track seasonal canopy development and photosynthesis, determine phenological transition dates, and estimate intra-annual and interannual variability in canopy photosynthesis. We used 59 site-years of camera imagery and net ecosystem exchange measurements from 17 towers spanning three plant functional types (deciduous broadleaf forest, evergreen needleleaf forest, and grassland/crops) to derive color indices and estimate gross primary productivity (GPP). GPP was strongly correlated with greenness derived from camera imagery in all three plant functional types. Specifically, the beginning of the photosynthetic period in deciduous broadleaf forest and grassland/crops and the end of the photosynthetic period in grassland/crops were both correlated with changes in greenness; changes in redness were correlated with the end of the photosynthetic period in deciduous broadleaf forest. However, it was not possible to accurately identify the beginning or ending of the photosynthetic period using camera greenness in evergreen needleleaf forest. At deciduous broadleaf sites, anomalies in integrated greenness and total GPP were significantly correlated up to 60 days after the mean onset date for the start of spring. More generally, results from this work demonstrate that digital repeat photography can be used to quantify both the duration of the photosynthetically active period as well as total GPP in deciduous broadleaf forest and grassland/crops, but that new and different approaches are required before comparable results can be achieved in evergreen needleleaf forest.
Journal Article
Biogeographical diversification of mainland Asian Dendrobium (Orchidaceae) and its implications for the historical dynamics of evergreen broad‐leaved forests
AIM: Evergreen broad‐leaved forests (EBLFs) occupy most tropical and subtropical regions of mainland Asia and exhibit high species diversity, productivity and richness. Understanding the historical dynamics of EBLFs is important for biodiversity conservation and regional carbon storage and cycling under global climate change. However, little is known about the historical dynamics of EBLFs in mainland Asia. Dendrobium, an epiphytic orchid genus found in EBLFs, was used to gain new insights of the historical establishment and extension of EBLFs in mainland Asia. LOCATION: Mainland Asia. METHODS: We sampled c. 80% of the currently recognized species of Dendrobium found in mainland Asia. A phylogeny was generated using maximum parsimony, maximum likelihood and Bayesian inference methods. A calibrated chronogram was obtained using a Bayesian relaxed‐clock model approach. Biogeographical scenarios were investigated using the statistical dispersal–vicariance analysis and dispersal–extinction–cladogenesis methods. Ancestral states were constructed by mesquite and bayestraits, and diversification of Dendrobium was investigated by APE and LASER packages. RESULTS: Our results indicate that Asian Dendrobium was present on mainland Asia since the Oligocene, after which this genus diversified in this region and dispersed into higher elevations. The ancestral habit of Dendrobium was epiphytic and terrestrial and lithophytic habits each have multiple, recently independent origins. MAIN CONCLUSIONS: Our results support the hypothesis that EBLFs have been established in mainland Asia at least since the Oligocene and further suggest that the EBLFs of mainland Asia expanded into higher elevations prior to the late Cenozoic. The diversification of Asian Dendrobium coincided with a warmer climate during the late Oligocene and middle Miocene and the expansion of key groups (including Fagaceae, Lauraceae, Magnoliaceae and Theaceae) of EBLFs during the early Cenozoic.
Journal Article
Habitat heterogeneity explains mosaics of evergreen and deciduous trees at local-scales in a subtropical evergreen broad-leaved forest
Questions: Mosaics of evergreen and deciduous trees that are characteristic of evergreen broad-leaved forests (EBLF) are thought to arise from habitat heterogeneity, but empirical evidence for this is limited. We test this assertion asking: (1) whether environmental heterogeneity explains the distribution of deciduous and evergreen trees; (2) which are the most important environmental variables; and (3) does their importance change with scale? Location: Tiantong National Forest Park, Ningbo, Zhejiang, China. Methods: We used data from a 20-ha individual-mapped EBLF in spatial point-pattern analyses testing the scale of aggregation within, and segregation between, the two life forms. We used a heterogeneous Poisson process model to remove the effects of environmental heterogeneity, predicting segregation would disappear if the mosaic was due to habitat heterogeneity alone. Finally, we tested the relative importance of theoretically important environmental variables using multivariate regression trees at three spatial scales (10, 20 and 50 m grid cells). Results: We found evergreen and deciduous trees were aggregated at scales below 125 m and 60 m, respectively, and mutually exclusive at scales <120 m. Evidence of any spatial segregation between the life forms was removed at all scales after controlling for environmental heterogeneity. Only soil phosphorus concentrations contributed to spatial patterns at all scales, with values >0.27-0.30 g·kg⁻¹ favouring deciduous species. Conclusions: Our study is consistent with habitat heterogeneity creating the observed mosaics of evergreen and deciduous tree species, but micro-habitat heterogeneity contributed even at scales <20 m. Soil phosphorus availability appears to be the major environmental variable maintaining these mosaic patterns at hillslope scales in EBLF.
Journal Article
Degradation of litter quality and decline of soil nitrogen mineralization after moso bamboo (Phyllostachys pubscens) expansion to neighboring broadleaved forest in subtropical China
Aims Moso bamboo (Phyllostachys pubescens) is a typical native invasive plant imposing serious threats on ecosystem processes and functions. A primary concern is alterations of litter and soil N mineralization in evergreen broadleaved forests coupled with bamboo population expansion. Methods We conducted a field study to determine the litter production, quality, N resorption efficiency, and soil N mineralization rates in bamboo-dominated forest (BDF) and adjacent uninvaded evergreen broadleaved forest (EBF) in subtropical China. Results The mean annual litter production for BDF was 5.82 Mg ha⁻¹, 36.0 % lower than that for EBF (9.09 Mg ha⁻¹). Litter N concentration was also lower, but C: N was higher after bamboo expansion, coupled with higher N resorption efficiency for Moso bamboo and lower litterfall, resulting in potential N return decreasing as much as 60.41 kg N ha⁻¹ yr⁻¹ to the soil. The soil N net nitrification and mineralization rates exhibited lower values in BDF than in EBF. In addition, annual soil N mineralization rate was positively correlated with litter production but negatively with C: N ratio of litter. Conclusions Expansion of bamboo into neighboring EBF decreased litter production and quality, reduced soil N mineralization rate, and ultimately retarded N cycling. These effects should be carefully considered in the design of restoration strategies for ecosystems impacted by bamboo species.
Journal Article
Contrasting patterns and drivers of soil fungal communities in subtropical deciduous and evergreen broadleaved forests
Subtropical broadleaved forests play a crucial role in supporting terrestrial ecosystem functions, but little is known about their belowground soil fungal communities despite that they have central functions in C, N, and P cycles. This study investigated the structures and identified the drivers of soil fungal communities in subtropical deciduous and evergreen broadleaved forests, using high-throughput sequencing and FUNGuild for fungal identification and assignment to the trophic guild. Fungal richness was much higher in the deciduous than in the evergreen forest. Both forests were dominated by
Ascomycota
and
Basidiomycota
phyla, but saprophytic fungi were more abundant in the deciduous forest and ectomycorrhizal fungi predominated in the evergreen forest. Fungal communities had strong links to plant and soil properties. Specifically, plant diversity and litter biomass were the main aboveground drivers of fungal diversity and composition in the deciduous forest, while host effects were prominent in the evergreen forest. The belowground factors, i.e., soil pH, water content, and nutrients especially available P, were identified as the primary drivers of soil fungal communities in the broadleaved forests. Co-occurrence network analysis revealed assembly of fungal composition in broadleaved forest soils was non-random. The smaller modularity of the network in the deciduous forest reflects lower resistance to environment changes. Concluding, these results showed that plant community attributes, soil properties, and potential interactions among fungal functional guilds operate jointly on the divergence of soil fungal community assembly in the two broadleaved forest types.
Journal Article