Herbivore resistance in congeneric and sympatric Nothofagus species is not related to leaf habit

Climate gradient and leaf carbon investment influence the effects of climate change on water use efficiency of forests: A meta-analysis

Forest ecosystems cover a large area of the global land surface and are important carbon sinks. The water-carbon cycles of forests are prone to climate change, but uncertainties remain regarding the magnitude of water use efficiency (WUE) response to climate change and the underpinning mechanism driving WUE variation. We conducted a meta-analysis of the effects of elevated CO2 concentration (eCO2 ), drought and elevated temperature (eT) on the leaf- to plant-level WUE, covering 80 field studies and 95 tree species. The results showed that eCO2 increased leaf intrinsic and instantaneous WUE (WUEi, WUEt), whereas drought enhanced both leaf- and plant-level WUEs. eT increased WUEi but decreased carbon isotope-based WUE, possibly due to the influence of mesophyll conductance. Stimulated leaf-level WUE by drought showed a progressing trend with increasing latitude, while eCO2 -induced WUE enhancement showed decreasing trends after >40° N. These latitudinal gradients might influence the spatial pattern of climate and further drove WUE variation. Moreover, high leaf-level WUE under eCO2 and drought was accompanied by low leaf carbon contents. Such a trade-off between growth efficiency and defence suggests a potentially compromised tolerance to diseases and pests. These findings add important ecophysiological parameters into climate models to predict carbon-water cycles of forests.

Phenology explains different storage remobilization in two congeneric temperate tree species with contrasting leaf habit

The dependence of trees on carbon and nutrient storage is critical to predicting the forest vulnerability under climate change, but whether evergreen and deciduous species differ in their use and allocation of stored resources during spring phenology is unclear. Using a high temporal resolution, we evaluated the role of spring phenology and shoot growth as determinants of the carbon and nutrient storage dynamics in contrasting leaf habits. We recorded the phenology and shoot elongation and determined the concentrations of total non-structural carbohydrates (NSCs), starch, soluble carbohydrates, nitrogen (N) and phosphorus (P) in buds, expanding shoots and previously formed shoots of two sympatric Nothofagus species with contrasting leaf habit. Species reached similar shoot lengths, though shoot expansion started 35 days earlier and lasted c. 40 days more in the deciduous species. Thus, although the deciduous species had a relatively constant shoot growth rate, the evergreen species experienced a conspicuous growth peak for c. 20 days. In the evergreen species, the greatest decreases in NSC concentrations of previously formed shoots and leaves coincided with the maximum shoot expansion rate and fruit filling, with minimums of 63 and 65% relative to values at bud dormancy, respectively. In contrast, minimum NSC concentrations of the previously formed shoots of the deciduous species were only 73% and occurred prior to the initiation of shoot expansion. Bud N and P concentrations increased during budbreak, whereas previously formed shoots generally did not decrease their nutrient concentrations. Late spring phenology and overlapping of phenophases contributed to the greater dependence on storage of proximal tissues in the studied evergreen compared with deciduous species, suggesting that phenology is a key determinant of the contrasting patterns of storage use in evergreen and deciduous species.

Phytochemical Screening and Antioxidant Activity of Seven Native Species Growing in the Forests of Southern Chilean Patagonia

The genus Nothofagus is one of the most abundant in the subantarctic Patagonian forests. Five species inhabit these ecosystems, three evergreen (Nothofagus betuloides, Nothofagus dombeyi, and Nothofagus nitida) and two deciduous (Nothofagus pumilio and Nothofagus antarctica). This is the first report on the levels of secondary metabolites and the antioxidant capacity of Patagonian tree species growing in natural environments. The aim of this work was to carry out a phytochemical screening, to determine the antioxidant capacity, the sun protection factor, and the α-glucosidase and tyrosinase inhibitory activity of foliar extracts of the five previous species. Besides, Aristotelia chilensis and Berberis microphylla, two species of Patagonian shrubs growing in the same forests, were used as reference. N. dombeyi was the Nothofagus with the best antioxidant capacity. B. microphylla differed from all studied species. Moreover, the Nothofagus was split into two groups. N. betuloides and N. dombeyi are the most similar species to A. chilensis. The α-glucosidase was completely inhibited by all studied extracts. Furthermore, N. antarctica, N.pumilio, and N. nitida inhibited about 70% of the tyrosinase activity. All the results found in this study for the species of the genus Nothofagus support further research on their potential beneficial properties for human health.

Relationships between population traits, nonstructural carbohydrates, and elevation in alpine stands of Vaccinium myrtillus

PREMISE

Despite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant-plant interaction, and elevation.

METHODS

We studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs.

RESULTS

Glucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue.

CONCLUSIONS

We found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands.

Secondary leaves of an outbreak-adapted tree species are both more resource acquisitive and more herbivore resistant than primary leaves

The magnitude and frequency of insect outbreaks are predicted to increase in forests, but how trees cope with severe outbreak defoliation is not yet fully understood. Winter deciduous trees often produce a secondary leaf flush in response to defoliation (i.e., compensatory leaf regrowth or refoliation), which promotes fast replenishment of carbon (C) storage and eventually tree survival. However, secondary leaf flushes may imply a high susceptibility to insect herbivory, especially in the event of an ongoing outbreak. We hypothesized that in winter deciduous species adapted to outbreak-driven defoliations, secondary leaves are both more C acquisitive and more herbivore resistant than primary leaves. During an outbreak by Ormiscodes amphimone F. affecting Nothofagus pumilio (Poepp. & Endl.) Krasser forests, we (i) quantified the defoliation and subsequent refoliation by analyzing the seasonal dynamics of the normalized difference vegetation index (NDVI) and (ii) compared the physiological traits and herbivore resistance of primary and secondary leaves. Comparisons of the NDVI of the primary and second leaf flushes relative to the NDVI of the defoliated forest indicated 31% refoliation, which is close to the leaf regrowth reported by a previous study in juvenile N. pumilio trees subjected to experimental defoliation. Primary leaves had higher leaf mass per area, size, carbon:nitrogen ratio and soluble sugar concentration than secondary leaves, along with lower nitrogen and starch concentrations, and similar total polyphenol and phosphorus concentrations. In both a choice and a non-choice bioassay, the leaf consumption rates by O. amphimone larvae were significantly higher (>50%) for primary than for secondary leaves, indicating higher herbivore resistance in the latter. Our study shows that secondary leaf flushes in outbreak-adapted tree species can be both C acquisitive and herbivore resistant, and suggests that these two features mediate the positive effects of the compensatory leaf regrowth on the tree C balance and forest resilience.