Linking drought-induced xylem embolism resistance to wood anatomical traits in Neotropical trees.

Drought-induced xylem embolism is considered to be one of the main factors driving mortality in woody plants worldwide. Although several structure-functional mechanisms have been tested to understand the anatomical determinants of embolism resistance, there is a need to study this topic by integrating anatomical data for many species. We combined optical, laser, and transmission electron microscopy to investigate vessel diameter, vessel grouping, and pit membrane ultrastructure for 26 tropical rainforest tree species across three major clades (magnoliids, rosiids, and asteriids). We then related these anatomical observations to previously published data on drought-induced embolism resistance, with phylogenetic analyses. Vessel diameter, vessel grouping, and pit membrane ultrastructure were all predictive of xylem embolism resistance, but with weak predictive power. While pit membrane thickness was a predictive trait when vestured pits were taken into account, the pit membrane diameter-to-thickness ratio suggests a strong importance of the deflection resistance of the pit membrane. However, phylogenetic analyses weakly support adaptive coevolution. Our results emphasize the functional significance of pit membranes for air-seeding in tropical rainforest trees, highlighting also the need to study their mechanical properties due to the link between embolism resistance and pit membrane diameter-to-thickness ratio. Finding support for adaptive coevolution also remains challenging.

Xylem anatomy needs to change, so that conductivity can stay the same: xylem adjustments across elevation and latitude in Nothofagus pumilio.

BACKGROUND AND AIMS: Plants have the potential to adjust the configuration of their hydraulic system to maintain its function across spatial and temporal gradients. Species with wide environmental niches provide an ideal framework to assess intraspecific xylem adjustments to contrasting climates. We aimed to assess how xylem structure in the widespread species Nothofagus pumilio varies across combined gradients of temperature and moisture, and to what extent within-individual variation contributes to population responses across environmental gradients. METHODS: We characterized xylem configuration in branches of N. pumilio trees at five sites across an 18° latitudinal gradient in the Chilean Andes, sampling at four elevations per site. We measured vessel area, vessel density and the degree of vessel grouping. We also obtained vessel diameter distributions and estimated the xylem-specific hydraulic conductivity. Xylem traits were studied in the last five growth rings to account for within-individual variation. KEY RESULTS: Xylem traits responded to changes in temperature and moisture, but also to their combination. Reductions in vessel diameter and increases in vessel density suggested increased safety levels with lower temperatures at higher elevation. Vessel grouping also increased under cold and dry conditions, but changes in vessel diameter distributions across the elevational gradient were site-specific. Interestingly, the estimated xylem-specific hydraulic conductivity remained constant across elevation and latitude, and an overwhelming proportion of the variance of xylem traits was due to within-individual responses to year-to-year climatic fluctuations, rather than to site conditions. CONCLUSIONS: Despite conspicuous adjustments, xylem traits were coordinated to maintain a constant hydraulic function under a wide range of conditions. This, combined with the within-individual capacity for responding to year-to-year climatic variations, may have the potential to increase forest resilience against future environmental changes.

Spatial variation of vessel grouping in the xylem of Betula platyphylla Roth.

Vessel grouping in angiosperms may improve hydraulic integration and increase the spread of cavitations through redundancy pathways. Although disputed, it is increasingly attracting research interest as a potentially significant hydraulic trait. However, the variation of vessel grouping in a tree is poorly understood. I measured the number of solitary and grouped vessels in the xylem of Betula platyphylla Roth. from the pith to the bark along the water flow path. The vessel grouping parameters included the mean number of vessels per vessel group (VG), percentage of solitary vessels (SVP), percentage of radial multiple vessels (MVP), and percentage of cluster vessels (CVP). The effects of cambial age (CA) and flow path-length (PL) on the vessel grouping were analyzed using a linear mixed model.VG and CVP increased nonlinearly, SVP decreased nonlinearly with PL. In trunks and branches, VG and CVP decreased nonlinearly, and SVP increased nonlinearly with CA. In roots, the parameters had no change with CA. MVP was almost constant with PL or CA. The results suggest that vessel grouping has a nonrandom variation pattern, which is affected deeply by cambial age and water flow path.

The evolution and function of vessel and pit characters with respect to cavitation resistance across 10 Prunus species.

Various structure-function relationships regarding drought-induced cavitation resistance of secondary xylem have been postulated. These hypotheses were tested on wood of 10 Prunus species showing a range in P50 (i.e., the pressure corresponding to 50% loss of hydraulic conductivity) from -3.54 to -6.27 MPa. Hydraulically relevant wood characters were quantified using light and electron microscopy. A phylogenetic tree was constructed to investigate evolutionary correlations using a phylogenetically independent contrast (PIC) analysis. Vessel-grouping characters were found to be most informative in explaining interspecific variation in P50, with cavitation-resistant species showing more solitary vessels than less resistant species. Co-evolution between vessel-grouping indices and P50 was reported. P50 was weakly correlated with the shape of the intervessel pit aperture, but not with the total intervessel pit membrane area per vessel. A negative correlation was found between P50 and intervessel pit membrane thickness, but this relationship was not supported by the PIC analysis. Cavitation resistance has co-evolved with vessel grouping within Prunus and was mainly influenced by the spatial distribution of the vessel network.

Anatomy basis and clinical significance of various types of abductor hallucis superior margin arterial arcades / Bases anatómicas e importancia clínica de varios tipos de arcos arteriales del margen superior del músculo abductor del hálux

The aim of this study was to group arteries of arterial arch at the superior margin of the abductor hallucis muscle according to their constitutes and provide anatomical basis for reverse bifolicated flap based on it. The constitute, track-way and distribution of the artery, which supply the medial pedis flap, the medial plantar and the medial tarsal flap, especial the arterial arch at the superior margin of the abductor hallucis muscle were observed and analyzed on 81 lower limbs cast specimens and 2 fresh feet specimens. According to their constitute, arterial arch at the superior margin of the abductor hallucis muscle can be classified into 3 types: i) type I, It was constituted mainly by the branch of anterior medial malleolus artery and (or) the medial tarsal artery. ii) type II, It was constituted mainly by the superficial branch of the medial plantar artery; iii) type II, It was constituted mainly by the branch of anterior medial malleolus artery and the branch of medial tarsal artery anastomose with the superficial branch of the medial plantar artery, which was divided into two subtypes according to the different anastomosis of the artery: Type III 1, the type of anastomosed directly was about 48.2 percent, type III 2, The type of anastomosed indirectly was about 24.1 percent. According to the constitute of arterial arch at the superior margin of the abductor hallucis muscle can be classified into three types: The type of anterior medial malleolus artery and medial tarsal artery, the type of superficial branch of the medial plantar artery and the type of mixed. For the type mixed, two subtypes can be classified according to the different anastomosis of the artery.

El objetivo fue clasificar las arterias de arco arterial del margen superior del músculo abductor del hálux según su constitución, y proporcionar una base anatómica para el colgajo bilobulado reverso basado en él. La constitución, recorrido y distribución de las arterias que suministran los colgajos pedicular medial, plantar medial y medial del tarso, en especial el arco arterial del margen superior del músculo abductor del hálux fueron observados y analizados en 81 modelos de miembros inferiores y 2 pies frescos. De acuerdo con su constitución, el arco arterial del margen superior del músculo abductor del hálux se pueden clasificar en 3 tipos: i) tipo I, constituido principalmentepor la rama de la arteria anterior del maléolo medial y/o la arteria medial del tarso. ii) tipo II, constituido principalmente por la rama superficial de la arteria plantar medial, iii) tipo III constituido principalmente por la rama de la arteria maleolar medial anterior y la rama de la anastomosis de la arteria tarsiana medial de la rama superficial de la arteria plantar medial, que se divide en 2 subtipos diferentes de acuerdo con el tipo de anastomosis: tipo III 1, una anastomosis directa que se observó en el 48,2 por ciento, y tipo III 2, una anastomosis indirecta observada en aproximadamente el 24,1 por ciento de los casos. Según la constitución, el arco arterial del margen superior del músculo abductor del hálux se puede clasificar en 3 tipos: el tipo de arteria anterior del maléolo medial y la arteria tarsiana medial, el tipo de rama superficial de la arteria plantar medial y el tipo mixto. En el tipo mixto, pueden ser clasificados 2 subtipos de acuerdo a la diferente anastomosis de la arteria.