Grasslands & Droughts

Montane grasslands stability under drought: the effect of functional diversity and alternative sources of water

Tropical Mountain Grassland at the Itatiaia National Park (RJ.Brazil) - Photo credit: I. S. Matos.

Montane grasslands at the Itatiaia National Park (RJ, Brazil) - Photo credit: I. S. Matos

MOTIVATION

Unveiling the factors underlying differential stability across biological systems remains one of the most fundamental questions in Ecology. Considering the worldwide increase in drought intensity, duration and frequency, the main goal of my Ph.D. research project was to investigate the role of two factors (1) the functional diversity (diversity on species response to disturbances and/or stresses), and (2) the use of alternative water sources (e.g. fog) on plants responses to drought. Since grasslands cover a large proportion of the terrestrial land surface and their productivity is strongly controlled by precipitation levels, those factors were evaluated particularly on grassland stability.

My Ph.D. thesis was divided in the following six chapters:

CHAPTER 1

Deciphering ecological stability of grasslands productivity in response to experimental droughts

Rainout shelter covering the montane grassland vegetation at the Itatiaia National Park (RJ, Brazil) - Photo credit: I. S. Matos.

We conducted a meta-analysis of rainfall manipulative experiments performed on 101 grasslands around the world to determine the relative importance of experimental drought features (intensity, frequency, duration) and prevailing climatic conditions (mean annual temperature, mean annual precitipation and rainfall seasonality) in explaining differential stability across sites [Click here to read the full paper].

CHAPTER 2

Critical transitions in rainfall manipulation experiments

Scheme for critical transitions in grasslands triggered by drought events - Image credit: I. S. Matos.

While conducting this meta-analysis, we realized that rainfall manipulative experiments performed to date have disregarded the possibility of droughts to trigger critical (non-reversible) transitions in grasslands. Therefore, we provided a step-by-step guide on how to design experiments to test for critical transitions. We also highlighted the implications of this new experimental approach when assessing and managing grasslands stability in response to natural droughts [Click here to read the full paper].

CHAPTER 3

Integrating eco-physiological strategies and functional originality indices to predict plant community stability in response to droughts

Scheme representing distinct eco-physiological strategies of response to drought found in a Tropical Mountain Grassland community - Photo credit: I. S. Matos.

By integrating eco-physiological strategies and functional originality indices, we provided a new conceptual framework to predict plant community functional stability under distinct scenarios of species loss. This framework was applied, using a Brazilian Tropical Mountain Grassland vegetation as a model system (Itatiaia National Park, RJ, Brazil), and it proved useful to identify the most vulnerable species, and thus, to assign conservation priorities [Click here to read the full paper].

CHAPTER 4

Who are the leaf water uptakers? Determining leaf traits that influence atmospheric water absorption by plants

Water droplets on a leaf of Achyrocline satureioides (Asteracea) at the Bocaina National Park (SP, Brazil) - Photo credit: I. S. Matos.

We investigated which leaf traits explain the interspecific variation in species capacity for foliar water uptake (FWU) - that is, species ability to absorb water through their leaf surfaces under dry conditions [Click here to read the chapter abstract].

CHAPTER 5

Retain or repel? Droplet volume does matter when measuring leaf wetness traits

Leaf wetness traits: A-B leaf water repellency; C-D leaf water retention - Photo credit: I. S. Matos.

We tested if changes in the droplet water volume could significantly affect the measurement of two leaf wetness traits (1) leaf water repellency - a measure of water spreadness on the leaf surface, and (2) leaf water retention - a measure of water adherence on the leaf surface. We also evaluated whether these traits could be used as proxies to predict species ability to perform foliar water uptake [Click here to read the full paper].

CHAPTER 6

Tropical montane grasslands responses to additive effects of El niño and climate change

The 3-month centred running monthly mean anomalies in standard deviation units (σ) for precipitation (Precip.), air temperature (Tair) at 1 PM and atmospheric vapour pressure deficit (VPD) at 1 PM for a tropical montane grassland at the Itatiaia National Park. Anomalies are shown for Jan 2014 to Aug 2017 period, thus encompassing the strong El Niño 2015/16 event and the moderate La Niña 2017. The magnitude of the El Niño/La Niña events is indicated by the El Niño 3.4 index (EN3.4 anomaly), represented by the vertically coloured gradient in the background. - Image credit: S. Rifai.

We investigated plant drought responses during and after the extreme 2015/16 El Niño event in 12 species with contrasting drought strategies (tolerance, avoidance and escape) in a Brazilian tropical montane grassland. We tested if (1) the El Niño event induced meteorological drought anomalies, (2) if the atmospheric and/or soil drought led to plant water stress and (3) if, plants showed signs of drought recovery. In contrast to other tropical areas, we found that the 2015/16 El Niño event did not strongly affect precipitation in our study site. However, it increased air temperature and vapour pressure deficit, thus pushing all grassland species, even the most drought-tolerant ones, beyond their hydraulic safety margins during the dry season. Most species showed signs of drought recovery, returning to positive hydraulic margins in the wet season after the El Niño. However, the finding that all evaluated species, regardless of their drought-response strategy, are already operating close to their hydraulic safe thresholds for stomatal closure and turgor loss suggests that this cool–humid tropical montane grassland is especially vulnerable to meteorological extremes exacerbated by the additive effects of El Niño and climate change. [Click here to read the full paper].

GENERAL CONCLUSIONS

Although grasslands showed resilient to drought in terms of above-ground biomass, their functional diversity migh be unstable. In a future with more droughts and less fog, resistant species could outperform non-resistant ones, leading to a functional homogenisation. Future experiments should subject vegetation to more extreme droughts, in order to test those predictions and to develop a better understanding about the mechanisms underlying differential stability across biological systems.

Tropical Mountain Grassland at the Itatiaia National Park (RJ.Brazil) - Photo credit: I. S. Matos.

76 PLANT SPECIES FROM THE TROPICAL MOUNTAIN GRASSLAND

Family and scientific name of the 76 plant species from the Itatiaia National Park (RJ, Brazil), which I have studied during my PhD research: ALSTROEMERIACEAE: 1. Alstroemeria foliosa Mart. ex Schult. & Schult.f.; 2. Alstroemeria isabelleana Herb.; AMARYLLIDACEAE: 3. Hippeastrum morelianum Lem.; APIACEAE: 4. Eryngium glaziovianum Urb.; APOCYNACEAE: 5. Oxypetalum glaziovii (E. Fourn.) Fontella & Marquete; ASTERACEAE: 6. Achyrocline satureioides (Lam.) DC.; 7. Baccharis altimontana G. Heiden et al.; 8. Baccharis brevifolia DC.; 9. Baccharis glaziovii Baker; 10. Baccharis grandimucronata Malag.; 11. Baccharis itatiaiae Wawra; 12. Baccharis parvidentata Malag.; 13. Baccharis pseudomyriochepala Malag; 14. Baccharis retusa DC.; 15. Baccharis stylosa Gardner; 16. Baccharis tarchonanthoides DC.; 17. Baccharis uncinella DC.; 18. Chaptalia runcinate Kunth; 19. Chionolaena capitate (Baker) Freire; 20. Gamochaeta purpurea (L.) Cabrera; 21. Graphistylis itatiaiae (Dusén) B. Nord.; 22. Grazielia gaudichaudiana (DC) R.M. King & H. Rob; 23. Hieracium commersonii Monnier; 24. Hypochaeris lutea (Vell.) Britton; 25. Leptostelma maximum D.Don; 26. Leptostelma tweediei (Hook &Arn) DJN Hind & GL Nesom; 27. Mikania camporum B.L. Rob.; 28. Mikania glaziovii Baker; 29. Senecio adamantinus Bong; 30. Senecio nemoralis Dusén; 31. Senecio oleosus Vell.; 32. Stevia camporum Baker; 33. Trixis glaziovii Baker; 34. Symphyopappus reitzii (Cabrera) R.M.King & H.Rob. BROMELIACEAE: 35. Fernseea itatiaiae (Wawra) Baker; CAMPANULACEAE: 36. Lobelia camporum Pohl; CARYOPHYLLACEAE: 37. Cerastium dicrotrichum Fenzl ex Rohrb.; CYPERACEAE: 38. Machaerina ensifolia (Boeckeler) T. Koyama; ERICACEAE: 39. Agarista hispidula (DC.) Hook. Ex. Nied.; 40. Gaultheria serrata (Vell.) Sleumer ex Kin.-Gouv.; 41. Gaylussacia amoena Cham.; 42. Gaylussacia chamissonis Meisn.; 43. Gaylussacia fasciculata Gardner; ERIOCAULACEAE: 44. Paepalanthus itatiaiensis Ruhland; ESCALLONIACEAE: 45. Escallonia laevis (Vell.) Sleumer; FABACEAE: 46. Lupinus gilbertianus C.P.Sm.; 47. Mimosa itatiaiensis Dusén; 48. Mimosa monticola Dusén.; GERANIACEAE: 49. Geranium brasiliense Progel; IRIDACEAE: 50. Gelasine coerulea (Vell.) Ravenna; 51. Sisyrinchium alatum Hook.; 52. Sisyrinchium nidulare (Hand. Mazz.) I.M. Johnst.; LAMIACEAE: 53. Lepechinia speciosa (A.St.Hil. ex Benth.) Epling; LENTIBULARIACEAE: 54. Utricularia reniformis A St.-Hill; MELASTOMATACEAE: 55. Tibouchina sebastianopolitana Cogn.; 56. Leandra quinquedentata (DC.) Cogn.; 57. Pleroma hospita (Schrank et Mart. ex DC.) Triana; MYRTACEAE: 58. Myrceugenia alpigena (DC.) Landrum; ONAGRACEAE: 59. Fuchsia campos-portoi Pilg. & Schulze-Menz; ORCHIDACEAE: 60. Pelexia itatiayae Schltr.; OROBANCHACEAE: 61. Esterhazya splendida J.C. Mikan; OXALIDACEAE: 62. Oxalis confertissima A.St.-Hil. PLANTAGINACEAE: 63. Plantago australis Lam.; 64. Plantago guilleminiana Decne POACEAE: 65. Chascolytrum itatiaiae (Ekman) Essi, Longhi-Wagner & Souza-Chies; 66. Chusquea pinifolia (Nees) Nees; 67. Cortaderia modesta (Döll.) Hack; POLYGALACEAE: 68. Polygala brasiliensis L.; 69. Polygala campestris Gardner; PRIMULACEAE: 70. Myrsine gardneriana A. DC.; PROTEACEAE: 71. Roupala montana Aubl.; ROSACEAE: 72. Fragaria vesca L.; RUBIACEAE: 73. Coccocypselum condalia Pers.; 74. Coccocypselum cordifolium Nees. & Mart.; 75. Galium humile Cham. &Schltdl.; SYMPLOCACEAE: 76. Symplocos itatiaiae Wawra - Photo credit: I. S. Matos.

FUNDING

Me at my favourite environment: mountains! Summit of the Agulhas Negras mountain located at the Itatiaia National Park (RJ, Brazil) - Photo credit: F. Barbosa.

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