Trees最新文献

Oak cotyledons are hypogeal and non-photosynthetic. Animal predation on cotyledons during the seedling stage is a very common phenomenon and may hinder oak forest regeneration. However, no studies have compared the effects of cotyledon loss on shoot and root growth, as well as mineral or nonstructural carbohydrate (NSC) storage, under different soil fertility conditions, making it difficult to identify whether root or shoot traits are the most reliable indicators for assessing the effects of cotyledon predation on seedling recruitment. We subjected Quercus variabilis seedlings to fifteen cotyledon removal times and two fertilization levels to measure cotyledon resource decrease kinetics and seedling mass at early growth stages and subsequent seedling performance at the end of first year. Cotyledon resource remobilization completed at 32 days after emergence, with phosphorus and NSC remobilizing more efficiently than nitrogen and potassium. Soil nutrients had no impact on cotyledon resource remobilization and early seedling growth. Cotyledon removal imposed stronger negative effects on root growth and storage than on shoots at the end of first year, which can be alleviated by fertilization. Cotyledon removal after 14 days of emergence did not decrease seedling growth and storage. In conclusion, cotyledon resources are more important than soil nutrients for early seedling growth, and early cotyledon removal greatly hinders subsequent seedling growth and storage, with roots being more sensitive to cotyledon removal than shoots. To improve oak seedling regeneration, cotyledons should be protected from animal predation at least 14 days after emergence by setting up a fence around acorns.

The vascular cambium is a key lateral meristem responsible for secondary growth in woody plants, producing secondary xylem and phloem. Understanding its activity is crucial for studies on plant phenology, carbon sequestration, and environmental responses. However, defining the precise period of cambial activity remains challenging due to reliance on indirect indicators, such as cambial zone width or the presence of undifferentiated cells adjacent to the cambium. These parameters often misrepresent the true timing of cambial cell division, conflating it with subsequent differentiation processes. This study critically examines the limitations of indirect indicators and advocates for a more precise definition of cambial activity strictly as the process of cellular division. Direct cellular markers, such as mitotic figures, phragmoplasts, and newly formed tangential walls, provide more accurate assessment of cambial activity. By distinguishing cell division from differentiation, we can refine growth periodicity analyses and improve our understanding of environmental influences on cambial function. We review the structure and activity of the vascular cambium, demonstrating how indirect indicators can misrepresent cambial activity dynamics and lead to errors in determining its onset, duration, and cessation. By integrating direct cellular markers, we propose a more accurate methodology for assessing cambial activity, improving phenological studies and providing a clearer framework for evaluating plant responses to climatic variability.

Tree mortality rates are increasing globally. Yet the finer-scale processes driving these patterns remain poorly understood. A deeper understanding of these mechanisms is critical for predicting forest responses to gradual climatic changes. Abies nephrolepis (Trautv. ex Maxim.) Maxim., a common coniferous tree species in the subalpine or boreal forests, has exhibited widespread mortality in old-growth stands. To investigate this phenomenon, we characterized the mortality spatial pattern of A. nephrolepis using data collected from two sites with varying elevations and slopes in the Mudanfeng Natural Reserve, China. Mark connection functions revealed that mortality labels (“dead” vs. “surviving”) were randomly distributed among all fir trees, consistent with a spatially random point process. Trivariate random labeling analyses indicated no influence of neighboring trees, either conspecific or heterospecific, on mortality patterns. Bivariate difference pair correlation functions provided no evidence for density-dependent mortality. However, mortality exhibited clear size dependence. We conclude that the random spatial distribution of tree sizes drove the random mortality pattern, with physiological senescence likely serving as the primary underlying mechanism.

Key message

Rolled sun leaves of Fagus sylvatica L. showed strong heterogeneous light acclimation of the photosynthetic apparatus across the leaf lamina as reflected in blue light excited chlorophyll fluorescence.

Abstract

Many grasses, but also dicotyledonous species have rolled leaves, which is interpreted as a resistance mechanism against drought. Rolled leaves intercept less light, which causes a reduced heat load but may also induce an acclimation of the photosynthetic apparatus to reduced irradiance. We have investigated the light acclimation of different parts of permanently rolled leaves of beech (Fagus sylvatica L.) using various methods based on chlorophyll fluorescence as well as by HPLC analysis of photosynthetic pigments. Chlorophyll fluorescence emission excited by blue light showed a strong heterogeneity across the leaf lamina, with the highest emission in the upward bent sides of the leaf and minimal emission in the center and tip of the lamina. Heterogeneity was absent in flat shade leaves and the flat sun leaves of another beech tree and also in all types of leaves when red light was used for fluorescence excitation. Since blue-induced fluorescence intensity was negatively correlated with the pool size of the violaxanthin cycle, it is concluded that the heterogeneity in blue light-excited fluorescence was caused by the variation of these carotenoid pigments across the leaves. Also light saturated electron transport rate and sensitivity to photoinhibition indicated shade acclimation of the upward bent leaf sides. It is concluded that leaf rolling in beech leaves may also have a photoprotective function.

Key message

This study reveals intraspecific variability in physiological and anatomical traits among tree species in different restinga formations, highlighting their adaptability to changing microclimatic conditions.

Abstract

Climate change, with increasingly frequent drought episodes, threatens the survival of tree species in biodiverse ecosystems like the Atlantic Forest. We investigated whether plants of the same species in different restinga formations exhibit intraspecific variability in physiological and secondary xylem traits. We evaluated five individuals of each of three tree species (Scutia arenicola (Casar.) Reissek (Rhamnaceae), Schinus terebinthifolia Raddi (Anacardiaceae), and Pera glabrata (Schott) Baill. (Peraceae) all of which co-occur across three distinct formations within the restinga of northern Rio de Janeiro State: a beach grass and shrub, a Clusia formation, and a sandbanks forest formation. We used standard methods of plant physiology and anatomy to study the traits, focusing on the structure–function relationships between leaf and secondary xylem. The evaluated species exhibited a set of variations in functional traits. While the leaves invested in water-use efficiency, the wood remained conservative, prioritizing hydraulic safety. These traits vary mainly in the Clusia and beach grass and shrub formations, where the canopy is open and both soil moisture availability and irradiance are lower and higher, respectively. In the sandbanks forest, where the canopy is closed and soil moisture is higher, a pattern of photosynthetic efficiency, carbon acquisition, and water transport efficiency was observed. The physiological and tissue variation identified in this study may have played a role in the coexistence of the species, allowing them to adjust to variable microclimates among the different restinga formations. This variation may be essential for the persistence of these species, enabling efficient water to use and safety, which is reflected in their maintenance along vegetation gradients over time and under future climate scenarios.

Mountain ecosystems are dynamic and highly sensitive to the negative impacts of climate change. Within this study, we conducted the first comprehensive dendrochronological, multi-site and multi-elevational study of Persian oak (Quercus brantii Lindl.) across the Zagros Mountains in Western Iran. Besides total ring-width (TRW), we separately measured earlywood width (EWW) and latewood width (LWW) to analyze climate impact on oak growth with sub-annual resolution. We found strong correlations between TRW, EWW, and LWW, as well as between the individual site chronologies. Several negative extreme events and long-term growth patterns were captured by all site chronologies, revealing an increase in the frequency of negative extreme events during recent decades (1930–2022). The standard chronologies exhibited strong climate signals representative for larger areas in West Asia and the Mediterranean region. Climate-growth response analyses indicated that winter precipitation is the most important growth-limiting factor, having a strong positive effect on the growth of the native oak species. Conversely, we found negative correlations between Tmax and Tmean and TRW, EWW, and LWW of Persian oak during the previous and current growth years. Correlations with various drought indices confirmed the strong negative impacts of dry periods on oak forests, particularly for the central and southern parts of the Zagros Mts. The very homogenous growth response across elevation and different microsite conditions emphasizes the dominant role of macroclimate on oak growth. Correlation analysis between annual and sub-annual ring-width parameters of Q. brantii and climate indices highlights the strong effect of large-scale teleconnection patterns on the Zagros oak forests. Our findings highlight the pivotal role of sufficient winter precipitation supply. Therefore, watershed management that promotes soil moisture conservation under current and expected future climate change is recommended to ensure long-term resilience of Persian oak forests.

Alnus glutinosa (L.) Gaertn is a crucial component of riparian ecosystems. Yet, many of its habitats are currently under threat, particularly in the southern regions of its distribution in Morocco. To effectively address the conservation and management of this species, it is imperative to gain a comprehensive understanding of various aspects of the species’ reproductive biology. The main objective of this study was to assess the viability and fertility of Alnus glutinosa (L.) Gaertn pollen grains using four tests: acetocarmine staining, Alexander staining, 2.3.5-triphenyltetrazolium chloride (TTC), and in vitro germination. Eleven representative populations of this species were carefully selected for analysis. The study revealed that Alnus glutinosa trees produce pollen with good cytoplasmic conformation, as exhibited by the acetocarmine (86.4%) and Alexander staining (74.45%). However, these tests tend to overestimate pollen viability, as estimates by the TTC enzymatic test (48.88%) and in vitro germination (4.5%) are significantly lower. Viability varied significantly both among and within populations. The results suggest that some trees produce sterile pollen. The observed variability in pollen viability between populations appears to be linked to environmental factors.

Key message

Climate sensitivity of Pinus sylvestris has changed in minimum density while maximum density remains mostly stable, suggesting the use of additional density parameters could help detect response changes.

Abstract

As one of Eurasia's most widely distributed conifer species, Pinus sylvestris L. is frequently used in dendroclimatological reconstructions based on tree-ring width (TRW) and maximum latewood density (MXD). However, the climatic signals of additional parameters such as earlywood/latewood density (EWD/LWD) or minimum density (MND) are often overlooked, leaving their skill unexplored. Here, we investigate the growth responses of multiple P. sylvestris tree-ring parameters to ongoing climate change at two sites with contrasting climatic conditions using well-replicated density data from Scotland and Sweden. Correlations with mean, minimum, and maximum temperatures are strongest for LWD and MXD at both sites, with coefficients ranging from 0.5 to 0.7 for July, August, and the June–August season (p < 0.05). A significant (p < 0.05) negative correlation between MND and July temperatures was identified in the Swedish Torneträsk (TOR) data (p < 0.05), which diminished since the late twentieth century. A comparable inverse MND temperature signal and change into the twenty-first century is not reflected in northern Scotland’s overall wetter and warmer site, suggesting a fundamental physiological change in tree-ring formation under global warming. A shift in the sensitivity of tree growth at northern European sites could reduce the effectiveness of proxies from such locations, posing implications for high-resolution climate reconstructions.

Key message

Long-term monitoring revealed nutrient- and site-specific changes of European beech foliar chemistry in correlation with meteorological conditions, underscoring shifts in beech nutrition due to climate change, thereby informing adapted sustainable forest management.

Abstract

Systematic long-term studies assessing the relevant macro- and micronutrients will improve our understanding of the complex interplay between climatic as well as site-specific factors and nutrient dynamics of European beech forests. Thus, we assessed the impact of meteorological conditions on the nutrition of old-growth European beech stands at a calcareous and an acidic site in central Germany. Foliar concentrations of six macronutrients and four micronutrients were analyzed over 13 years (2009–2021), and their association with meteorological conditions depending on the site was assessed using a linear mixed-effects model. The results revealed nutrient-specific and, for half of the nutrients, site-specific responses to meteorological variables, that is, mean annual temperature (MAT) and precipitation (MAP) of the current and/or the previous year. Within the MAT range of the observational period (7.4–10.3 °C), for nitrogen (calcareous site), phosphorus, magnesium, sulfur, copper, and zinc, a nonlinear relationship was observed, that is, the nutrient concentrations increased until a temperature optimum and decreased thereafter. In contrast, the concentrations of potassium (calcareous site), manganese, and iron increased and of calcium decreased with increasing temperature. MAP (351–723 mm) had an impact on the concentration of six nutrients (nitrogen, potassium, calcium, copper, iron, and zinc), but its effect was generally smaller than that of MAT. Our results indicate that the persistent deficiencies in foliar phosphorus (calcareous site) and sulfur (acidic site) may be aggravated with ongoing climate change. The findings may guide site-specific sustainable and ecosystem-oriented forest management strategies for the future.

Key message

Successive droughts impacted Nothofagus dombeyi trees in Patagonia, with irreversible growth decline in trees with higher levels of partial crown mortality. This indicates a negative legacy effect that persists beyond the drought periods.

Abstract

Globally, more frequent and severe droughts are driving increased tree crown defoliation, loss of vigor, and tree mortality, having detrimental effects on forest structure and functioning. This is the case of N. dombeyi, a broadleaf evergreen species, that has strongly suffered from negative drought-induced impacts during the last century. Here we analyzed differences in long-term growth trends, post-drought and post-wetness responses, drought legacies, and early warning signals of co-occurring healthy, apparently non-healthy (partial crown mortality), and dead N. dombeyi trees growing in northern Patagonia. Trees experienced growth reductions under selected droughts but recovered their pre-drought growth level when the drought ended. Trees with partial crown mortality levels exceeding 50%, and dead trees, exhibited significant growth decline. Growth decline was associated with reduced growth and a negative long-term post-drought response. This highlighted an irreversible decrease towards the more recent droughts, indicating a state change which denotes a negative legacy effect. The occurrence of successive dry and wet years during the last decades shaped the growth trend of healthy N. dombeyi trees, but resulted less informative for trees with higher crown mortality levels. Similarly, regular early warning metrics did not emerge as strong predictors of vigor loss. The study sheds light on the multifaceted factors influencing crown dieback dynamics, and underscores the need for further research on tree health and resilience.