Background and Aims

Plant photosystem thermal thresholds are regularly used as indicators for plant tolerance under extreme temperature scenarios. Photosystem tolerance can vary with species, leaf traits and environmental conditions. To date, most research into plant thermal tolerance has been conducted on established plants; likewise, leaf traits are routinely measured on fully expanded, adult leaves. To fully understand function and survival of plant communities, the first leaves of early life stages must be considered.

Methods

We sought to understand germinant photosystem thermal tolerance breadth through upper and lower critical temperature (T_crit) thresholds, leaf mass per area (LMA) and leaf water content (LWC) for 22 species from three contrasting biomes – extreme desert and alpine, and benign coastal temperate. For seven of these species, we compared the relationship between these traits with those of older juvenile and adult life stages.

Key Results

Biome of origin had no effect on germinant thermal thresholds. Thermal tolerance breadth (heat minus cold tolerance thresholds) varied significantly among germinant species, but not across the three life stages. However, although germinant heat tolerance within species was comparable to adult thermal tolerance, germinants were significantly less cold tolerant than adults. LMA was greater in older life stages than in germinants, LWC decreased across the life stages. LMA was greater in older life stages than in germinants and LWC decreased as LMA increased.

Conclusions

In the first known study examining photosystem thermal tolerance breadth of newly emerged leaves of germinants, we found germinant PSII to be as heat tolerant as later life stages, but less cold tolerant, associated with their lower LMA and higher LWC. This demonstrates that not all physiological aspects of germinant tolerance are more vulnerable to thermal extremes than older life stages, with certain leaf traits potentially playing an important role in early survival.

Script and data for:

Alvarez et al. Fresh out of the seed coat: first leaves of germinants are equally heat tolerant but are less cold tolerant than later life stages

Contains 26 files"

(1) Analysis - R scripts required to replicate analysis and figures in the manuscript material (6 file total):

DRYAD_germinant_biome_and_species_analysis.R

DRYAD_figure_1.R

DRYAD_figure_2.R

DRYAD_figure_3.R

DRYAD_Life_stages_traits_comparison.R

DRYAD_traits_compared_at_life_stages.R

(2) Datasets (20 files total):

dfcold.csv

dfhot.csv

dfttb.csv

For the analysis comparing biome Tcrit hot, cold and thermal tolerance breadth.

Columns:

	biome - temperate, desert, alpine

	species - Acacia aneura, Acacia binervata, Acacia longifolia, Acacia salicina, Acacia victoriae, Aciphylla glacialis, Banksia integrifolia, Capparis mitchellii, Carex appressa, Carex gaudichaudina, Ceratopetalum apetalum, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Melaleuca hypericifolia, Oxylobium ellipticum, Pittosporum undulatum, Senna artemisioides, Stylidium montanum, Viola betonicifolia			

        germ_temp - temperature seeds were germinated in: 10/5, 15/5, 20/20, 25/15, 30/20, 35/25, 40/30 (max/min; °C)	

	block - replicate; 1,2,3,4,5

	tcrit - the inflection point between the fast and slow rise phases of the T- F0 curve (Knight and Ackerly 2002)

	agegroups - the age the germinants were (in days) at time of measurement

	pretreatment - the treatment given to seeds prior to germination to break dormancy or allow for ease of germination; scarfication, cold stratification, wing removal



TTB_figure.csv

For graphing the thermal tolerance breadth of germinants

Columns:

	biome - temperate, desert, alpine

  	species - Acacia aneura, Acacia binervata, Acacia longifolia, Acacia salicina, Acacia victoriae, Aciphylla glacialis, Banksia integrifolia, Capparis mitchellii, Carex appressa, Carex gaudichaudina, Ceratopetalum apetalum, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Melaleuca hypericifolia, Oxylobium ellipticum, Pittosporum undulatum, Senna artemisioides, Stylidium montanum, Viola betonicifolia	

	tcrit_run - cold, hot

	mTTB - mean thermal tolerance breadth

	mTol - mean tolerance

	sdTTB - standard deviation thermal tolerance breadth

	sdTol- standard deviation tolerance

	nTTB - number of thermal tolerance breadth measurements

	nTol- number of tolerance measurements

	seTTB - standard deviation thermal tolerance breadth

	seTol - standard deviation tolerance

Leaf_traits.csv

For graphing the leaf traits of germinants

Columns:

	biome - temperate, desert, alpine

  	species - Acacia aneura, Acacia binervata, Acacia longifolia, Acacia salicina, Acacia victoriae, Aciphylla glacialis, Banksia integrifolia, Capparis mitchellii, Carex appressa, Carex gaudichaudina, Ceratopetalum apetalum, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Melaleuca hypericifolia, Oxylobium ellipticum, Pittosporum undulatum, Senna artemisioides, Stylidium montanum, Viola betonicifolia	

	LMA - leaf mass per area (g m–2)

	water_content - water content of the leaves (g g−1)

LMA.csv

water_content.csv

Tcrit_hot.csv

Tcrit_cold.csv

Tcrit_TTB.csv

Life_stages_traits_comparison.csv

For analysing and graphing trait differences across life stages

Columns:

 	species - Acacia aneura, Acacia salicina, Acacia victoriae, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Oxylobium ellipticum, Senna artemisioides

	biome - temperate, desert, alpine

	stage - germinant, juvenile, adult

	LMA - leaf mass per area (g m–2)

	water_content - water content of the leaves (g g−1)

	tcrit_hot - the inflection point in hot temperatures (°C) between the fast and slow rise phases of the T- F0 curve (Knight and Ackerly 2002) 

	tcrit_cold - the inflection point in cold temperatures (°C) between the fast and slow rise phases of the T- F0 curve (Knight and Ackerly 2002) 

	tcrit_TTB- the difference between the hot and cold inflection points in hot and cold temperatures (°C) between the fast and slow rise phases of the T- F0 curve (Knight and Ackerly 2002)

germinants_hot.csv

germinants_cold.csv

germinants_ttb.csv

juveniles_hot.csv

juveniles_cold.csv

juveniles_ttb.csv

adults_hot.csv	

adults_cold.csv

adults_ttb.csv

For analysing

	biome - temperate, desert, alpine

	species - 

Germinants: Acacia aneura, Acacia binervata, Acacia longifolia, Acacia salicina, Acacia victoriae, Aciphylla glacialis, Banksia integrifolia, Capparis mitchellii, Carex appressa, Carex gaudichaudina, Ceratopetalum apetalum, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Melaleuca hypericifolia, Oxylobium ellipticum, Pittosporum undulatum, Senna artemisioides, Stylidium montanum, Viola betonicifolia

Juveniles: Acacia aneura, Acacia binervata, Acacia longifolia, Acacia salicina, Dodonaea viscosa,Eucalyptus largiflorens, Eucalyptus pauciflora,Flindersia maculosa, Oxylobium ellipticum

Adults: Acacia aneura, Acacia salicina, Acacia victoriae, Dodonaea viscosa, Eucalyptus coolabah, Eucalyptus largiflorens, Eucalyptus pauciflora, Flindersia maculosa, Oxylobium ellipticum, Senna artemisioides

	tcrit - the inflection point between the fast and slow rise phases of the T- F0 curve (Knight and Ackerly 2002)

	LMA - leaf mass per area (g m–2)

	water_content - water content of the leaves (g g−1)

Fresh out of the seed coat: first leaves of germinants are equally heat tolerant but are less cold tolerant than later stages

Data files

Abstract

Fresh out of the seed coat: first leaves of germinants are equally heat tolerant but are less cold tolerant than later stages

Data files

Abstract

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