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Spring leaf phenology is an important event for trees to determine carbon fixation during the growing season. However, less is understood about the intraspecific variation in spring leaf phenology and its relationship with the spring temperature requirements of conifers, which is problematic for accurately predicting the influence of spring climate warming on conifers. I monitored bud burst timing and the degree days required for bud burst for seedlings and large individuals of Abies sachalinensis (fir) and Larix kaempferi (larch) over two seasons in northern Japan. Contrary to my expectation, the degree days required for the bud burst of small individuals were similar to or larger than those of the large individuals for fir and larch. Consequently, the bud burst timing of small individuals was similar to or later than that of large individuals for fir and larch. Even when conifer species are in their early stage, the spring temperature requirement for bud burst is not necessarily less than that for large individuals, which is not the case for many broad-leaved species. These results indicate that for these two coniferous species, ontogenetic differences in temperature requirements are not necessary to be considered for the response of communities to spring climate change.

Yield prediction has been determined to be vital in sustainable forest management. Recently, research trends have shifted from stand-level to individual-level yield prediction. In this study, we examined the effectiveness of yield prediction models based on a distance-independent approach for Japanese cedar (Cryptomeria japonica (L.f.) D.Don) trees in western Japan. We further examined the accuracy of the models with reference to existing data collected over the long-term. First, we constructed distance-independent height, diameter growth, and survival models. Then, we simulated for approximately 50 years individual tree height, diameter at breast height (DBH), and volume growth using the test data. We then compared the predicted and observed values and calculated root-mean-square error (RMSE) and bias to evaluate the model accuracy. The models were noted to perform well when predicting mean height, DBH, and volume for Japanese cedar trees; in fact, they adequately predicted the diameter distribution. Our results suggest that distance-independent models could adequately predict long-term mean values and diameter distribution. However, RMSE and bias indicated that error propagation occurred over longer time spans. Thus, it is effective to conduct actual measurements at some point in the forest development phase and use the measurements as initial values for short- or medium-term predictions.

International audience; Water deficit or drought is the most important abiotic stress limiting plant growth performance and plant community development; this is typical in the Mediterranean area where plants are often severely and permanently water limited. Such is the case of the argan tree (Argania spinosa (L.) Skeels), one of the tree species most affected by desertification and global warming. To advance knowledge on how this tree can withstand drought stress, inoculation with a native complex of arbuscular mycorrhizal fungi (AMF), composed mainly of the genus Glomus, was studied in connection with a set of growth and physiological parameters. Under controlled conditions, inoculated and non-inoculated argan seedlings were grown for 3 months under three water regimens: 25%, 50%, and 75% relative to the field capacity of used soil substrate. The results showed that the argan tree had different growth abilities to develop and withstand the various applied water limitations. The AMF complex stimulated the growth and mineral nutrition of argan seedlings under the different imposed levels of water deficiency. Relative water content (RWC) in leaves, water potential, and stomatal conductance in argan leaves showed a general improvement in inoculated seedlings compared to non-inoculated ones. Soluble sugar and proline contents significantly increased in non-inoculated seedlings compared with inoculated seedlings under water-limiting conditions (25%). Similarly, oxidative enzyme (catalase, peroxidase, superoxide dismutase) activity increased significantly in drought-stressed seedlings. Non-inoculated seedlings showed the highest accumulation of these enzymes. Moreover, mycorrhizal symbiosis establishment positively correlated with argan tree seedlings in terms of growth, mineral nutrition, soluble sugar and proline contents, and enzymes activities. The main results from the current study suggest that AMF improve the ability of A. spinosa to tolerate drought by enhancing mineral nutrition and the transport of high levels of water by enhancing the RWC and water potential in leaves. Finally, the alleviation of the destructive effects of reactive oxygen species was modulated by enzymatic scavenging activity. Hence, the use of AMF in the technical process of argan seedlings production is highly recommended in different ecofriendly restoration strategies, with the aim of producing high quality seedlings capable of tolerating drought stress.; Le déficit hydrique ou la sécheresse est le stress abiotique le plus néfaste pour la croissance des plantes et le développement des communautés végétales, ce qui est typique en région méditerranéenne où les végétaux sont souvent sévèrement et en permanence privés d’eau. C’est le cas de l’arganier (Argania spinosa (L.) Skeels), une des espèces d’arbre parmi les plus affectées par la désertification et le réchauffement global. Pour élargir les connaissances sur la façon dont cet arbre peut résister au stress causé par la sécheresse, l’inoculation avec un complexe indigène de champignons mycorhiziens à arbuscules (CMA), composé surtout de champignons du genre Glomus, a été étudiée en lien avec un ensemble de paramètres physiologiques et de croissance. En conditions contrôlées, des semis d’arganier inoculés et non inoculés ont été soumis à trois régimes hydriques (25, 50 et 75 % de la capacité au champ du sol utilisé comme substrat) pendant trois mois. Les résultats montrent que l’arganier possède différentes capacités de croissance pour se développer et supporter les différents degrés de privation d’eau qui ont été appliqués. Le complexe de CMA a stimulé la croissance et la nutrition minérale des semis d’arganier malgré les différentes intensités de déficit hydrique. La teneur relative en eau dans les feuilles, le potentiel hydrique et la conductance stomatique dans les feuilles de l’arganier se sont généralement améliorés chez les semis inoculés comparativement aux semis non inoculés. La teneur en sucre soluble et en proline a significativement augmenté chez les semis non inoculés relativement aux semis inoculés dans les conditions d’irrigation restreinte (25 %). Cela était similaire aux enzymes oxydatifs (catalase, peroxydase, superoxyde dismutase) dont l’activité a significativement augmenté chez les semis stressés par la sécheresse. L’accumulation de ces enzymes a atteint un sommet chez les semis non inoculés. De plus, l’établissement de la symbiose mycorhizienne était positivement corrélé avec les semis d’arganier en termes de croissance, de nutrition minérale, de teneur en sucre soluble et d’activité enzymatique. Les principaux résultats qui découlent de cette étude indiquent que les CMA augmentent la tolérance à la sécheresse de l’arganier en améliorant la nutrition minérale et le transport de quantités élevées d’eau en augmentant la teneur relative en eau et le potentiel hydrique dans les feuilles. Finalement, l’atténuation des effets néfastes des types réactifs d’oxygène étaient modulés par l’activité de piégeage enzymatique. Par conséquent, l’utilisation des CMA dans l’itinéraire technique de production de semis d’arganier est fortement recommandée dans différentes stratégies de restauration respectueuses de l’environnement fondées sur l’arganier dans le but de produire des semis de grande qualité capables de tolérer le stress causé par la sécheresse.

We measured differences in %C, %N, δ13C, and δ15N of plant functional types (PFTs) between burned and unburned ground surfaces soon after a wildfire on a north-facing slope in interior Alaska. The C and N were measured for 16 species and Sphagnum litter. δ13C differed among the PFTs and was low for trees and shrubs, suggesting that woody stems slowed C dynamics or showed low water use efficiency. δ15N concentrations suggested that the herbaceous plants depended less on the mycorrhizal associations that became weak on the burned surfaces. The shrub leaves showed the lowest δ15N of PFTs and showed higher δ15N on the burned surface, showing that N transfer from the soils to the leaves in the shrubs was slowed by the wildfire. Mosses showed the highest C/N ratio. Sphagnum litter decomposed faster on the burned surface, and %N and δ15N in the litter increased from the second to third year on both burned and unburned surfaces, while %C changed little. In conclusion, the responses to the wildfire differed among the PFTs as characterized by their C and N dynamics.

Liaodong oak (Quercus liaotungensis Koidz.) dominated forests contribute to the few natural forest ecosystems in the semiarid Loess Plateau region in China. This study investigated the influence of soil nutrients and stand structure on aboveground net primary productivity (ANPP) in the oak communities. We aimed to understand the major factors and their possible pathways that determine the ecosystem productivity. The biomass and the ANPP were estimated using plot surveys and litterfall collection in fixed plots. Linear regressions and structural equation models were used to evaluate the relationships among soil nutrients, stand structure (including vertical and horizontal structure), and ANPP. The results showed that the effect sizes of soil nutrients on ANPP and leaf production were near 60% and 70%, respectively. More than 70% of the variation in woody production was explained by stand structure, while litterfall production was largely dependent on stand vertical structure with effect size of 64%. The effect of soil nutrients on stand structural indices was detected only in the case of the vertical structure. The results suggested that soil nutrients could affect forest productivity both directly and indirectly in coordination with stand vertical structure, and that the effect of stand structure was limited in these communities.

Wood-inhabiting fungi are critically important for the decomposition of coarse woody debris (CWD). To evaluate the relative importance of climate, vegetation, and spatial factors in the functional composition of fungal communities that inhabit CWD in discontinuously distributed subalpine Hondo spruce (Picea jezoensis (Sieb. & Zucc.) Carr. var. hondoensis (Mayr) Rehder) forests, a metabarcoding analysis was conducted on spruce deadwood samples obtained from six subalpine forests in central Japan using a high-throughput DNA sequencing technique. We detected 454 fungal operational taxonomic units (OTUs) from 67 spruce CWDs and determined that spatial factors explained a larger fraction of community variation than environmental (climate and vegetation) factors at all six study sites. However, environmental factors explained a larger fraction than spatial factors if we excluded data from one site that is geographically distant from other study sites. The OTU number and the occurrence of brown-rot fungi were positively associated with mean annual temperature and negatively associated with mean annual precipitation. Similarly, the principal component of forest vegetation significantly affected the OTU number and occurrence of brown-rot fungi. Precipitation seasonality was positively associated with the OTU number of undefined saprotrophs. These results suggest that fungal OTUs belonging to different functional groups respond differently to environmental variables.

Hondo spruce (Picea jezoensis var. hondoensis (Mayr) Rehder)) is separately distributed among several mountainous regions in central Japan as remnant populations of the last glacial period. To identify factors that affect Hondo spruce seedling regeneration on decaying logs, we investigated the relationships between climatic conditions, log properties, including decay type by fungi, and Hondo spruce seedling density on logs using data from seven subalpine Hondo spruce forests in central Japan. The results showed that the presence of soft rot was associated with higher seedling density, and the effect of brown rot in sapwood and white rot in heartwood on the predicted number of spruce seedlings on logs switched from positive to negative with increasing temperature and precipitation. Because soft rot occurs under humid conditions, the use of forest management techniques that increase the number of logs with soft rot in sapwood (e.g., by keeping the forest floor moist) are recommended for the sustainable regeneration of Hondo spruce. However, the relationships between wood decay type and seedling regeneration can also be affected by climate condition and thus are more complex than previously thought.

Climate extremes impact the function, structure, and composition of terrestrial ecosystems, while ecosystem responses to climate extremes differ with variations in frequency, intensity, and timing of the extreme event. We examined the canopy recovery processes following a typhoon disturbance in a cool–temperate deciduous forest in northern Japan based on 6-year data of canopy coverage imagery using a digital cover photography (DCP) approach that estimates canopy metrics relevant to leaf and woody masses, spatial dynamics, or arrangement of foliage elements. The DCP-derived imagery detected increases in leaf area index and foliage cover within 2∼3 years after the typhoon (i.e., recovery to the pre-typhoon state). Meanwhile, the recovery in leaf area and foliage cover observed after 6 years resulted from a spatial re-arrangement of the foliage elements (i.e., small within-crown gap fraction, foliage clumping) with increasing canopy space availability. Thus, the recovery of the spatial arrangement of foliage elements after the typhoon to the pre-typhoon state takes longer than the recovery of the leaf and woody masses. This study provides an important ecological implication in terms of possible resilience adaptation for ecosystem function and structure following extreme climate events.

Maire yew (Taxus chinensis var. mairei (Lemee et Levl) Cheng et L.K. Fu) is an endangered coniferous species in China. We examined the genetic pattern of Maire yew populations and explored any gene...