Phosphorus accumulation in Proteaceae seeds: a synthesis

Abstract

The family Proteaceae dominates the nutrient-poor, Mediterranean-climate floristic regions of southwestern Australia (SWA) and the Cape of South Africa. It is well-recognised that mediterranean Proteaceae have comparatively large seeds that are enriched with phosphorus (P), stored mainly as salts of phytic acid in protein globoids. Seed P can contribute up to 48% of the total aboveground P, with the fraction allocated depending on the species fire response. For SWA species, 70–80% of P allocated to fruiting structures is invested in seeds, compared with 30–75% for Cape species, with SWA species storing on average 4.7 times more P per seed at twice the concentration. When soil P is less limiting for growth, seed P reserves may be less important for seedling establishment, and hence plants there tend to produce smaller seeds with less P. For Australian Hakea and Grevillea species the translocation of P from the fruit wall to the seed occurs in the days/weeks before final fruit dry mass is reached, and accounts for 4–36% of seed P. Seed P content increases with the level of serotiny, though it decreases marginally as a fraction of the total reproductive structure. The greater occurrence of serotiny and higher seed P content within the Proteaceae in SWA supports the notion that SWA soils are more P-impoverished than those of the Cape.

Appendix 1

Seed phosphorus data for southwestern Australian and Cape of South Africa Proteaceae. Hakea data from the Cape represent naturalised populations. Nomenclature as used by the respective authors. For fire response: R = resprouts, K = fire-killed. For serotiny: 0 = non-serotinous, 1 = seeds retained 1–3 years (weakly serotinous), 2 = seeds retained >4 years (strongly serotinous).

	Fire response	Serotiny	Seed dry mass (mg)	P content (mg g-1)	Total P (mg)
SW Australia
B. attenuata a	R	2	89	10.4	0.89
B. burdettii a	K	2	34	10.2	0.34
B. chamaephyton a	R	2	116	6.6	0.81
B. coccinea b	K	1	14	10.0	0.14
B. hookeriana a	K	2	34	11.3	0.37
B. hookeriana b	K	2	38	12.0	0.46
B. hookeriana c	K	2	46	12.0	0.56
B. laricina d	K	2	22	12.3	0.26
B. menziesii a	R	1	78	12.1	0.94
B. menziesii c	R	1	88	12.0	1.05
B. prionotes a	K	1	23	11.8	0.27
B. prionotes c	K	1	25	13.0	0.33
B. scabrella a	K	2	30	11.5	0.34
B. speciosa c	K	2	114	10	1.14
Dryandra formosa b	K	1	10	9.9	0.10
Grevillea annulifera b	K	0	120	9.8	1.18
G. candelabroides e	K	0	23	14.8	0.34
G. eriostachya e	R	0	51	13.4	0.68
G. excelsior e	K	0	86	12.8	1.10
G. hookeriana e	K	0	43	13.4	0.57
G. leucopteris e	K	0	46	9.7	0.45
G. petrophiloides e	K	0	24	10.5	0.25
G. pinaster e	R	0	79	12.0	0.94
G. polybotrya e	K	0	31	12.5	0.39
G. tripartita e	K	0	45	6.1	0.27
G. wilsonii f	R	0	121	8.7	1.1
Hakea circumalata g	K	1	23	13.6	0.32
H. crassifolia c	K	2	129	11.0	1.42
H. erinacea h	K	1	12	11.7	0.14
H. lasianthoides i	K	1	20	17.9	0.14
H. obliqua c	K	2	27	16.0	0.44
H. recurva c	K	0	18	10.0	0.18
H. stenocarpa c	R	1	14	16	0.22
H. trifurcata h	K	1	16	12.2	0.20
H. undulata f	K	2	32	13.7	0.44
H. platysperma b	K	2	298	21.6	6.56
H. platysperma c	K	2	630	25	15.76
H. psilorrhyncha g	K	2	67	14.5	0.97
H. pycnoneura j	K	2	6t	36	0.21
H. victoria b	K	2	28	13.7	0.38
Xylomelum angustifolium b	R	2	756	19.6	14.82
South Africa
Aulax umbellata u	K	1	33v	2.5	0.08
Hakea drupacea k	K	2	34	13.4	1.12
H. sericea l	K	2	34r	11.7	0.40
H. sericea k	K	2	84	9.9	0.83
Leucadendron argenteum l	K	1	186r	1.1	0.20
L. coniferum m	K	1	13	9.0	0.11
L. gandogeri u	K	1	20v	5.0	0.10
L. linifolium u	K	1	12v	4.2	0.05
L. meridianum m	K	1	9	12.2	0.11
L. xanthoconus u	K	1	12v	6.9	0.08
Leucospermum cordifolium l	K	0	88r	1.9	0.17
L. conocarpodendron n	R	0	93	1.6	0.15
L. cuneiforme l	R	0	77r	1.9	0.15
L. oleifolium l	K	0	61r	1.8	0.11
L. parile l	K	0	18r	5.1	0.09
L. parile o	K	0	30	5.4	0.16
Protea compacta p	K	1	160	5.4	0.86
P. mundii l	K	1	65s	3.6	0.23
P. neriifolia l	K	1	22r	2.2	0.05
P. repens l	K	1	34r	1.8	0.06
P. repens p	K	1	82	4.6	0.38
P. obtusifolia q	K	1	30	7.2	0.22
P. obtusifolia m	K	1	23	10.7	0.25
P. susannae m	K	1	36	10.9	0.39

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