Nutrient resorption is associated with high leaf vein density and - - PowerPoint PPT Presentation

Nutrient resorption is associated with high leaf vein density and drives growth performance of dipterocarp tree species

Plant Ecophysiology Group, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences Mengla, Yunnnan, China (Email: zjl@xtbg.org.cn) Jiao-Lin Zhang, Shi-Bao Zhang, Ya-Jun Chen, Yi-Ping Zhang and L. Poorter

Outline

Introduction Materials and Methods Results Summary Acknowledgements

Definition:

Nutrient resorption is the process by which nutrients are translocated from senescing leaves to storage organs or growing tissues.

Significance:

Contribute a substantial percentage of the nitrogen (N) and phosphorus (P) used annually by plants (Ryan & Bormann, 1982) Makes a species less dependent on its current capacity for nutrient uptake (Aerts, 1996) Plant fitness and ecosystem nutrient cycling

Definition and significance of nutrient resorption

However, despite its pivotal role in the nutrient economy of plants and ecosystems, we know surprisingly little: Which plant traits drive nutrient resorption？ How resorption efficiency is associated with other leaf traits？ Whether nutrient resorption has an impact on plant performance？

Three processes concerning nutrient resorption:

Hydrolysis of N- (mainly protein ) and P- (nucleic acids + various P esters + lipids ) containing compounds in the leaves (amino acids + inorganic phosphates) Phloem loading Phloem transport Leaf vein density = Vein length per unit area Sack et al., 2012

Wright & Westoby 2003

Nutrient resorption and leaf economics spectrum

It has been postulated that increased nutrient resorption can increase plant growth performance, especially in nutrient-poor environments, there is a surprising paucity of studies that evaluate whether nutrient resorption matters at all for plant growth. To our knowledge there is no comparative study that directly showed whether enhanced nutrient resorption is indeed associated with increased plant growth (May & Killingbeck 1992).

Hypothesis

Nutrient resorption efficiency is positively related to

the phloem transport capacity, as indicated by a high leaf vein density；

Nutrient resorption efficiency is associated with

conservative leaf traits (such as high LMA, leaf thickness) that enhance leaf lifespan and nutrient residence time in the plants；

Nutrient resorption efficiency is positively related to

plant growth.

San Jose

Xishuangbanna Tropical Botanical Garden

1 2 3 4 5 6 7 8 9 10 11 12 50 100 150 200 250 300 350 10 15 20 25 30

Temperature (oC) Rainfall (mm)

MAT: 23.7 ℃ Precipitation: 1,560 mm Month

1 3 1 1 2 1

2

1 5 XTBG

17 species from 6 genera of Dipterocarpaceae

Nutrient resorption

N resorption efficiency P resorption efficiency N resorption proficiency P resorption proficiency

Nutrient stoichiometry

N concentration in green leaves P concentration in green leaves N/P ratio in green leaves N/P ratio in senesced leaves

Leaf anatomy and morphology

Vein density Leaf thickness Palisade mesophyll thickness Spongy mesophyll thickness Ratio of palisade to spongy mesophyll thickness Leaf mass per unit area Leaf density

Growth

Height growth rate Diameter growth rate

Traits measured in this study

Resorption efficiency:

Nitrogen resorption efficiency (NRE): NRE (%) = [(Ngr – Nsen) ⁄ Ngr] × 100 (Kobe et al. 2005) where Ngr and Nsen are the concentrations of N measured from mature green leaves and senesced leaves, respectively. Similar calculations were made for P resorption efficiency (PRE)

Resorption proficiency:

Nutrient resorption can also be described in terms of proficiency. N- and P resorption proficiency were defined as N and P concentrations in senesced leaves, respectively (cf. Killingbeck, 1996).

Anisoptera costata Dipterocarpus retusus Hopea hainanensis Parashorea chinensis Shorea assamica

Vatica xishuangbannaensis

Leaf venation

% 10 20 30 40 50 60

Hha VM HM HH VG PC SA VX HC DT2 SR DR DA SS DT1 AC DI NRE (%) 10 20 30 40 50 60 70 SR PC Hha DA DT1 VM HM HH VG SS SA DT2 DR VX HC DI AC PRE (%) 20 40 60 80

43% 53% NRE PRE Variation in NRE and PRE across species

% 10 20 30 40 50 60

Amazonian 48% 47% China Amazonian 53% 53.5% China

Arrangement of 17 traits along the first two principal component axes (PCA) after Varimax rotation, with construction based on species trait values for 17 dipterocarp species

Relationships of N and P resorption efficiencies with leaf vein density (a, d), leaf mass per unit area (b, e), leaf thickness (c, f) across 17 dipterocarp species

Relationships of N and P concentrations in senesced leaves with leaf vein density (a, d), leaf mass per area (b, e), and leaf thickness (c, f) across 17 dipterocarp species

Relationships of height- (a, b) and diameter (c, d) growth rates with N and P resorption efficiencies across 17 dipterocarp species

Summary

Hypothesis H1 Positive association of nutrient resorption efficiency with the phloem transport capacity Only NRE H2 Association of nutrient resorption efficiency with conservative leaf traits (such as high LMA, leaf thickness) Only NRE H3 Positive association of nutrient resorption efficiency with plant growth Only NRE

Acknow ledgements

National Natural Science Foundation of China Xishuangbanna Tropical Botanical Garden,

Chinese Academy of Sciences

Coauthors: Dr. Shi-Bao Zhang, Dr. Ya-Jun Chen,

• Dr. Yi-Ping Zhang and Dr. L. Poorter