Trees

This study provides a simple protocol for storage of alder clones. The technique described is useful for in vitro germplasm collections, decreasing the risk of genetic changes and associated costs. The aim of this study was to develop a simple method for the medium-term storage of Alnus glutinosa (L.) Gaertn. explants obtained from trees aged 20–30 years. Several parameters were evaluated, including type of explant (shoot apex or nodal segments), pre-storage treatment (0 or 10 days after the last subculture) and duration of cold storage (3–24 months) at 2–4 °C. Explants were maintained at this temperature under dim lighting on Woody Plant Medium supplemented with 0.1 mg l−1 6-benzyladenine and 0.5 mg l−1 indole-3-acetic acid. Under these conditions, a high percentage (75–87 %) of cultures remained viable after 18 months in cold cabinets. The stored material was successfully recovered and multiplied normally in the same medium, showing good growth and developing into normal shoots that were morphologically similar to those of non-stored controls. At the histological level, the main change observed was the accumulation of starch granules in cells of the shoot apex, as well as in cells located close to the vascular bundles, after 3 months of cold storage. As the duration of cold storage increased, the number and size of the starch granules decreased but cell plasmolysis and the content of lipid droplets increased. Cold damage was generalized after 24 months at 4 °C. This study provides new insights into the changes occurring in A. glutinosa during cold storage.

Stable carbon isotope composition varies markedly between sun and shade leaves, with sun leaves being invariably more enriched (i.e., they contain more13C). Several hypotheses have emerged to explain this pattern, but controversy remains as to which mechanism is most general. We measured vertical gradients in stable carbon isotope composition (δ13C) in more than 200 trees of nine conifer species growing in mixed-species forests in the Northern Rocky Mountains, USA. For all species except western larch, δ13C decreased from top to bottom of the canopy. We found that δ13C was strongly correlated with nitrogen per unit leaf area (N area), which is a measure of photosynthetic capacity. Usually weaker correlations were found between δ13C and leaf mass per area, nitrogen per unit leaf mass, height from the ground, or depth in the canopy, and these correlations were more variable between trees than for N area. Gradients of δ13C (per meter canopy depth) were steeper in small trees than in tall trees, indicating that a recent explanation of δ13C gradients in terms of drought stress of upper canopy leaves is unlikely to apply in our study area. The strong relationship between N area and δ13C here reported is consistent with the general finding that leaves or species with higher photosynthetic capacity tend to maintain lower CO2 concentrations inside leaves. We conclude that photosynthetic capacity is a strong determinant of δ13C in vertical canopy profiles, and must be accounted for when interpreting δ13C values in conifer forests.

Salinity reduces plant growth and crop production globally. The discovery of genes in salinity tolerant plants will provide the basis for effective genetic engineering strategies, leading to greater stress tolerance in economically important crops. In this study, we have identified and isolated 107 salinity tolerant candidate genes from a mangrove plant, Acanthus ebracteatus Vahl by using bacterial functional assay. Sequence analysis of these putative salinity tolerant cDNA candidates revealed that 65% of them have not been reported to be stress related and may have great potential for the elucidation of unique salinity tolerant mechanisms in mangrove. Among the genes identified were also genes that had previously been linked to stress response including salinity tolerance, verifying the reliability of this method in isolating salinity tolerant genes by using E. coli as a host.

We observed the formation of latewood tracheids with narrow diameters and thick walls and the disappearance of stored starch around the cambium on the locally heated region of stems in evergreen conifer Chamaecyparis pisifera during winter cambial dormancy. Wood formation is controlled by cambial cell division, which determines the quantity and quality of wood. We investigated the factors that control cambial activity and the formation of new tracheids in locally heated stems of the evergreen conifer Chamaecyparis pisifera. Electric heating tape was wrapped around one side of the stem, at breast height, of two trees in 2013 and two in 2014. Pairs of stems were locally heated in winter, and small blocks were collected from heated and non-heated regions of stems. Cambial activity and levels of stored starch around the cambium were investigated by microscopy. Cambial reactivation and xylem differentiation occurred earlier in heated than in non-heated regions. New cell plates were formed after 14–18 days of heating. After a few layers of tracheids with large diameters and thin walls had formed, cell division and cell enlargement during differentiation were inhibited. Tracheids with narrow diameters and thick walls, defining those as latewood, were formed near the cambium, and finally, four to six layers of tracheids were induced. After cambial reactivation, amounts of stored starch started to decrease and starch disappeared completely from phloem and xylem cells that were located near the cambium during the differentiation of heated regions. Our results suggest that an increase in temperature induces the conversion of stored starch to soluble sugars for continuous cambial cell division and earlywood formation. By contrast, a shortage of stored starch might be responsible for inhibition of cambial activity and induction of the formation of latewood tracheids.

In Sakhalin fir trees from nine different source elevation provenances, we found genetic differentiation of traits related to mechanical reinforcement, hydraulic efficiency, and photosynthetic capacity. Climatic conditions change with elevation and trees must cope with the resulting variation in stresses. Thus, trees may differentiate into elevational ecotypes with genetic-based variations in morphological and physiological traits. To explore genetically differentiated traits related to elevational adaptation, needles and stems were analyzed in 43-year-old Sakhalin fir [Abies sachalinensis (Fr. Schm.) Masters] trees which derived from nine source elevations (230–1250 m above sea level) and grown in a nursery plantation at 230 m above sea level. Trees from a high-elevation provenance showed greater mechanical reinforcement in needles and stems. Needles from high-elevation provenances were shorter and thicker, and developed more sclerenchyma in transfusion tissue. Shorter and thicker stems and larger reaction wood portions were also found. Moreover, needles and stems from high-elevation provenance trees also exhibited xylem traits associated with higher hydraulic efficiency and lower hydraulic safety. In the midrib xylem, the theoretical conductivity was greater due to higher number of tracheids. Pit architecture of stem-xylem tracheid indicated a higher hydraulic efficiency, but lower hydraulic safety due to larger pit apertures. Furthermore, high-elevation provenance trees exhibited a thicker bark, which may reduce water losses and act as a water reservoir in winter. Leaf nitrogen content and stomata number per needle were higher in high-elevation provenance trees, both of which were related to high photosynthetic capacity. Overall, the data suggested genetic differentiation of traits related to various trade-offs and optimization for mechanical resistance, hydraulic efficiency, and photosynthetic capacity at high elevation in Sakhalin fir.

Relatively little is known about changes in leaf attributes over the lifespan of woody plants. Knowledge of such changes may be useful in interpreting physiological changes with age. This study investigated changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans. Fully expanded leaves were sampled from the upper canopy of tree ages ranging from 6 to 240 years, and tree heights ranging from about 10–80 m. There were significant changes in leaf form with increasing tree age and height. Leaf size and specific leaf area (SLA; leaf area/leaf mass) decreased, leaf thickness increased, and leaves became narrower relative to their length, with increasing tree age and height. Cuticle thickness and leaf waxiness, including wax occlusion of the stomatal antechamber, increased with increasing age and height. By comparison, there were no clear trends in stomatal frequency or stomatal length with tree age, although there were curvilinear relationships between an index of total stomatal pore area per leaf lamina and both tree age and tree height. The results support the hypothesis that leaves of E. regnans become more xeromorphic with tree age and height. The results are discussed in relation to their significance for changes in water relations in the canopy with age.

Key message In an evergreen species with fixed-growth, warming advanced budburst but not leaf appearance and growth, and the further developed abnormal shoots by warming indicates extended growing season instead of leaf fall. Abstract We investigated the effects of warming and precipitation manipulation on phenology (spring phenology, leaf fall, and abnormal shoot phenology) in Pinus densiflora, which is an evergreen species with fixed-growth. In an open-air nursery, 2-year-old P. densiflora seedlings were planted in April 2013 and treated with 6 treatments (n = 3) [2 temperature levels: + 3 °C (TW) and control (TC); 3 precipitation levels: + 30% (PI), − 30% (PD), and control (PC)]. We observed spring and abnormal shoot phenology in 2014 and 2015, and measured dry weight of fallen leaves in 2015. Phenology was not changed by precipitation manipulation. In spring phenology, budburst was advanced by 9.4–9.6 days under warming, but timing of leaf appearance and growth did not changed. Cumulative weight of fallen leaves was 25.8–28.6% lower in TW plots than in TC plots between July and December 2015. There were no significant differences in occurrence rates of abnormal shoots among plots. 65.7–96.8% of abnormal shoots remained at the budburst stage in TC plots, while abnormal shoots in TW plots further developed to the leaf appearance and growth stages. Abnormal shoot development stopped 10.5–28.8 days later in TW plots than the TC plots in 2014 and 2015. Effects of warming were evident only in budburst, because leaf appearance and growth were affected by fixed-growth characteristics as well as warming. Decreased leaf fall and further developed abnormal shoots could be interpreted as delayed leaf senescence and extended growing season, respectively, for an evergreen species with fixed-growth.