title: Vascular performance of woody plants in a temperate rain forest: lianas suffer higher levels of freeze-thaw embolism than associated trees

authors: Jiménez-Castillo, Mylthon

subjects: liana distribution

abstract: The success of lianas in tropical rain forests has been linked to their wide xylem vessels that confer much higher hydraulic conductivity than tropical trees. In contrast, the poorer representation of lianas in temperate forests and high elevations might reflect lower competitiveness there, because of the vulnerability of high-performance xylem to freeze–thaw embolism. Nevertheless, the empirical evidence that support this idea is surprisingly scarce.
We assessed this hypothesis comparing the hydraulic performance of five lianas and nine trees coexisting in cold weather, by measuring wood traits, hydraulic conductivity, xylem embolism and root pressures.
Vessel diameters of lianas were on average twice those of trees (51·3 vs. 23·2 μm), resulting in an 18-fold difference in mean specific hydraulic conductivity (15·5 vs. 1·05 kg s−1 m−1 MPa−1). Lianas on average suffered higher levels of freeze–thaw embolism than trees (29·9 vs. 12·8%), reducing their potential hydraulically supported competitive advantage; however, partially embolized lianas still had greater water transport capacity than trees.
Specific hydraulic conductivity (Ks) was well correlated with vessel size in lianas but not in trees; however, plants with big vessels were more vulnerable to freeze embolism. Although all species of lianas developed root pressures and these tended to be higher than trees, root pressure were insufficient to repair embolism in plants > c. 7 m tall. The magnitudes of root pressure were well correlated with vessel size in lianas, but this relationship was not observed in trees.
Synthesis: Our results show empirical evidence that hydraulic performance of temperate lianas exceed the performance of coexisting trees, in similar magnitude than its tropical counterparts. Nevertheless, this hydraulic advantage is reduced as a consequence of freeze embolism. Temperate lianas appear to employ a bet-hedging strategy entailing significant embolism in winter, but likely enabling rapid carbon gain during frost-free periods. Loss of winter carbon gain opportunities because of embolism may explain the low success of lianas in temperate rain forest. However, predicted future climatic scenarios could are likely to increase liana abundance in mid-latitudes and allow lianas to expand their ranges towards higher latitudes and elevations.

text: Vascular performance of woody plants in a temperate rain forest: lianas suffer higher levels of freeze-thaw embolism than associated trees The success of lianas in tropical rain forests has been linked to their wide xylem vessels that confer much higher hydraulic conductivity than tropical trees. In contrast, the poorer representation of lianas in temperate forests and high elevations might reflect lower competitiveness there, because of the vulnerability of high-performance xylem to freeze–thaw embolism. Nevertheless, the empirical evidence that support this idea is surprisingly scarce.
We assessed this hypothesis comparing the hydraulic performance of five lianas and nine trees coexisting in cold weather, by measuring wood traits, hydraulic conductivity, xylem embolism and root pressures.
Vessel diameters of lianas were on average twice those of trees (51·3 vs. 23·2 μm), resulting in an 18-fold difference in mean specific hydraulic conductivity (15·5 vs. 1·05 kg s−1 m−1 MPa−1). Lianas on average suffered higher levels of freeze–thaw embolism than trees (29·9 vs. 12·8%), reducing their potential hydraulically supported competitive advantage; however, partially embolized lianas still had greater water transport capacity than trees.
Specific hydraulic conductivity (Ks) was well correlated with vessel size in lianas but not in trees; however, plants with big vessels were more vulnerable to freeze embolism. Although all species of lianas developed root pressures and these tended to be higher than trees, root pressure were insufficient to repair embolism in plants > c. 7 m tall. The magnitudes of root pressure were well correlated with vessel size in lianas, but this relationship was not observed in trees.
Synthesis: Our results show empirical evidence that hydraulic performance of temperate lianas exceed the performance of coexisting trees, in similar magnitude than its tropical counterparts. Nevertheless, this hydraulic advantage is reduced as a consequence of freeze embolism. Temperate lianas appear to employ a bet-hedging strategy entailing significant embolism in winter, but likely enabling rapid carbon gain during frost-free periods. Loss of winter carbon gain opportunities because of embolism may explain the low success of lianas in temperate rain forest. However, predicted future climatic scenarios could are likely to increase liana abundance in mid-latitudes and allow lianas to expand their ranges towards higher latitudes and elevations.

year: 2013

title: Is there a link between deep-sea biodiversity and ecosystem function?

authors: Leduc, Daniel

subjects: Challenger Plateau

abstract: Studying the diversity-ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity-ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep-sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity-function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity-ecosystem function relationship in the largest ecosystem on Earth.

text: Is there a link between deep-sea biodiversity and ecosystem function? Studying the diversity-ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity-ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep-sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity-function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity-ecosystem function relationship in the largest ecosystem on Earth.

year: 2013

title: Waiwharangi

authors: Maxwell, Te Kahautu

abstract: Haka. Lyrics/Musical score composed by Te Kahautu Maxwell. Performed by Ōpōtiki Mai Tawhiti (Kapa Haka group) (4mins)

Waiata: Tira Aroha
Whakaeke: Haere mai rā
Mōteatea: Te Pātere a Te Turuki
Poi: Iarararararī
Waiata ā ringa: Taku Mana Māori Motuhake
Haka: Waiwharangi
Whakawātea: Āio

text: Waiwharangi Haka. Lyrics/Musical score composed by Te Kahautu Maxwell. Performed by Ōpōtiki Mai Tawhiti (Kapa Haka group) (4mins)

Waiata: Tira Aroha
Whakaeke: Haere mai rā
Mōteatea: Te Pātere a Te Turuki
Poi: Iarararararī
Waiata ā ringa: Taku Mana Māori Motuhake
Haka: Waiwharangi
Whakawātea: Āio

year: 2020-02-06